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  <H5 align="left" style="page-break-before:always"><A HREF="#toc">Table of Contents</A></H5><P>
  <DIV style="font-family: 'Times New Roman',Times,serif">
  
  
  
  <DIV align="center" style="font-size: 10pt; margin-top: 18pt">As
  filed with the Securities and Exchange Commission on December 9, 2005
  </DIV>
  
  
  <DIV align="right" style="font-size: 10pt; margin-top: 12pt">Registration No.&nbsp;333-_____
  </DIV>
  
  
  <DIV style="width: 100%; border-bottom: 2pt solid black; font-size: 1pt">&nbsp;</DIV>
  <DIV style="width: 100%; border-bottom: 1pt solid black; font-size: 1pt">&nbsp;</DIV>
  
  
  
  
  <DIV align="center" style="font-size: 14pt; margin-top: 12pt"><B>SECURITIES AND EXCHANGE COMMISSION</B>
  </DIV>
  
  <DIV align="center" style="font-size: 12pt"><B>Washington, D.C. 20549</B>
  </DIV>
  
  <DIV align="center" style="font-size: 18pt; margin-top: 12pt"><B>FORM S-8</B>
  </DIV>
  
  
  <DIV align="center" style="font-size: 12pt; margin-top: 12pt"><B>REGISTRATION STATEMENT UNDER<BR>
  THE SECURITIES ACT OF 1933</B>
  </DIV>
  
  <DIV align="center" style="font-size: 24pt; margin-top: 12pt"><B>NxSTAGE MEDICAL, INC.</B>
  </DIV>
  
  <DIV align="center" style="font-size: 10pt">(Exact Name of Registrant as Specified in Its Charter)</DIV>
  
  
  <DIV align="center">
  <TABLE style="font-size: 10pt" cellspacing="0" border="0" cellpadding="0" width="100%">
  <!-- Begin Table Head -->
  <TR valign="bottom">
      <TD width="47%">&nbsp;</TD>
      <TD width="5%">&nbsp;</TD>
      <TD width="47%">&nbsp;</TD>
  </TR>
  
  <!-- End Table Head -->
  <!-- Begin Table Body -->
  <TR valign="bottom">
      <TD align="center" valign="top"><B>Delaware</B>
  </TD>
      <TD>&nbsp;</TD>
      <TD align="center" valign="top"><B>04-3454702</B></TD>
  </TR>
  <TR valign="bottom">
      <TD align="center" valign="top">(State or Other Jurisdiction of Incorporation
  </TD>
      <TD>&nbsp;</TD>
      <TD align="center" valign="top">(I.R.S. Employer</TD>
  </TR>
  <TR valign="bottom">
      <TD align="center" valign="top">or Organization)
  </TD>
      <TD>&nbsp;</TD>
      <TD align="center" valign="top">Identification No.)</TD>
  </TR>
  <TR valign="bottom"><!-- Blank Space -->
      <TD align="center" valign="top">&nbsp;</TD>
      <TD>&nbsp;</TD>
      <TD align="center" valign="top">&nbsp;</TD>
  </TR>
  <TR valign="bottom">
      <TD align="center" valign="top"><B>439 South Union Street</B>
  </TD>
      <TD>&nbsp;</TD>
      <TD align="center" valign="top"><B>01843</B></TD>
  </TR>
  <TR valign="bottom">
      <TD align="center" valign="top"><B>Lawrence, Massachusetts</B></TD>
      <TD>&nbsp;</TD>
      <TD align="center" valign="top">&nbsp;</TD>
  </TR>
  <TR valign="bottom">
      <TD align="center" valign="top">(Address of Principal Executive Offices)
  </TD>
      <TD>&nbsp;</TD>
      <TD align="center" valign="top">(Zip Code)</TD>
  </TR>
  <!-- End Table Body -->
  </TABLE>
  </DIV>
  
  <DIV align="center" style="font-size: 10pt; margin-top: 12pt"><B>1999 Stock Option and Grant Plan<BR>
  2005 Stock Incentive Plan<BR>
  2005 Employee Stock Purchase Plan</B><BR>
  (Full Title of the Plan)</DIV>
  
  <DIV align="center" style="font-size: 10pt; margin-top: 12pt"><B>Jeffrey H. Burbank<BR>
  President and Chief Executive Officer<BR>
  439 South Union Street<BR>
  Lawrence, Massachusetts 01843</B><BR>
  (Name and Address of Agent For Service)<BR>
  <B>(978)&nbsp;687-4700</B><BR>
  (Telephone Number, Including Area Code, of Agent For Service)</DIV>
  
  
  <DIV align="center" style="font-size: 10pt; margin-top: 18pt"><B>CALCULATION OF REGISTRATION FEE</B>
  </DIV>
  
  <DIV align="center">
  <TABLE style="font-size: 10pt" cellspacing="0" border="0" cellpadding="0" width="100%">
  <!-- Begin Table Head -->
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      <TD width="1%">&nbsp;</TD>
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      <TD width="1%">&nbsp;</TD>
      <TD width="5%">&nbsp;</TD>
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      <TD width="2%">&nbsp;</TD>
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      <TD width="5%">&nbsp;</TD>
      <TD width="1%">&nbsp;</TD>
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      <TD width="2%">&nbsp;</TD>
      <TD width="1%">&nbsp;</TD>
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      <TD width="2%">&nbsp;</TD>
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      <TD width="5%">&nbsp;</TD>
      <TD width="1%">&nbsp;</TD>
  
      <TD width="1%">&nbsp;</TD>
  </TR><TR style="font-size: 1px" valign="bottom">
      <TD nowrap align="left" colspan="21" style="border-bottom: 3px solid #000000">&nbsp;</TD>
  </TR>
  <TR style="font-size: 8pt" valign="bottom">    <TD width="1%">&nbsp;</TD>
  
      <TD>&nbsp;</TD>
      <TD style="border-right: 2px solid #000000">&nbsp;</TD>
      <TD>&nbsp;</TD>
      <TD>&nbsp;</TD>
      <TD>&nbsp;</TD>
      <TD>&nbsp;</TD>
      <TD style="border-right: 2px solid #000000">&nbsp;</TD>
      <TD>&nbsp;</TD>
      <TD nowrap align="center" colspan="2">Proposed</TD>
      <TD>&nbsp;</TD>
      <TD style="border-right: 2px solid #000000">&nbsp;</TD>
      <TD>&nbsp;</TD>
      <TD nowrap align="center" colspan="2">Proposed</TD>
      <TD>&nbsp;</TD>
      <TD style="border-right: 2px solid #000000">&nbsp;</TD>
      <TD>&nbsp;</TD>
      <TD nowrap align="center" colspan="2">&nbsp;</TD>
      <TD>&nbsp;</TD>
      <TD width="1%">&nbsp;</TD>
  </TR>
  <TR style="font-size: 8pt" valign="bottom">    <TD width="1%">&nbsp;</TD>
  
      <TD nowrap align="center">Title of</TD>
      <TD style="border-right: 2px solid #000000">&nbsp;</TD>
      <TD>&nbsp;</TD>
      <TD>&nbsp;</TD>
      <TD>&nbsp;</TD>
      <TD>&nbsp;</TD>
      <TD style="border-right: 2px solid #000000">&nbsp;</TD>
      <TD>&nbsp;</TD>
      <TD nowrap align="center" colspan="2">Maximum</TD>
      <TD>&nbsp;</TD>
      <TD style="border-right: 2px solid #000000">&nbsp;</TD>
      <TD>&nbsp;</TD>
      <TD nowrap align="center" colspan="2">Maximum</TD>
      <TD>&nbsp;</TD>
      <TD style="border-right: 2px solid #000000">&nbsp;</TD>
      <TD>&nbsp;</TD>
      <TD nowrap align="center" colspan="2">&nbsp;</TD>
      <TD>&nbsp;</TD>
      <TD width="1%">&nbsp;</TD>
  </TR>
  <TR style="font-size: 8pt" valign="bottom">    <TD width="1%">&nbsp;</TD>
  
      <TD nowrap align="center">Securities to be</TD>
      <TD style="border-right: 2px solid #000000">&nbsp;</TD>
      <TD>&nbsp;</TD>
      <TD nowrap align="center" colspan="2">Amount to be</TD>
      <TD>&nbsp;</TD>
      <TD style="border-right: 2px solid #000000">&nbsp;</TD>
      <TD>&nbsp;</TD>
      <TD nowrap align="center" colspan="2">Offering Price Per</TD>
      <TD>&nbsp;</TD>
      <TD style="border-right: 2px solid #000000">&nbsp;</TD>
      <TD>&nbsp;</TD>
      <TD nowrap align="center" colspan="2">Aggregate</TD>
      <TD>&nbsp;</TD>
      <TD style="border-right: 2px solid #000000">&nbsp;</TD>
      <TD>&nbsp;</TD>
      <TD nowrap align="center" colspan="2">Amount of</TD>
      <TD>&nbsp;</TD>
      <TD width="1%">&nbsp;</TD>
  </TR>
  <TR style="font-size: 8pt" valign="bottom">    <TD width="1%">&nbsp;</TD>
  
      <TD nowrap align="center">Registered</TD>
      <TD style="border-right: 2px solid #000000">&nbsp;</TD>
      <TD>&nbsp;</TD>
      <TD nowrap align="center" colspan="2">Registered(1)</TD>
      <TD>&nbsp;</TD>
      <TD style="border-right: 2px solid #000000">&nbsp;</TD>
      <TD>&nbsp;</TD>
      <TD nowrap align="center" colspan="2">Share</TD>
      <TD>&nbsp;</TD>
      <TD style="border-right: 2px solid #000000">&nbsp;</TD>
      <TD>&nbsp;</TD>
      <TD nowrap align="center" colspan="2">Offering Price</TD>
      <TD>&nbsp;</TD>
      <TD style="border-right: 2px solid #000000">&nbsp;</TD>
      <TD>&nbsp;</TD>
      <TD nowrap align="center" colspan="2">Registration Fee</TD>
      <TD>&nbsp;</TD>
      <TD width="1%">&nbsp;</TD>
  </TR>
  <TR style="font-size: 1px">
  
      <TD width="1%">&nbsp;</TD>
      <TD nowrap align="center">&nbsp;</TD>
      <TD style="border-right: 2px solid #000000">&nbsp;</TD>
      <TD>&nbsp;</TD>
      <TD nowrap align="center" colspan="2">&nbsp;</TD>
      <TD>&nbsp;</TD>
      <TD style="border-right: 2px solid #000000">&nbsp;</TD>
      <TD>&nbsp;</TD>
      <TD nowrap align="center" colspan="2">&nbsp;</TD>
      <TD>&nbsp;</TD>
      <TD style="border-right: 2px solid #000000">&nbsp;</TD>
      <TD>&nbsp;</TD>
      <TD nowrap align="center" colspan="2">&nbsp;</TD>
      <TD>&nbsp;</TD>
      <TD style="border-right: 2px solid #000000">&nbsp;</TD>
      <TD>&nbsp;</TD>
      <TD nowrap align="center" colspan="2">&nbsp;</TD>
      <TD>&nbsp;</TD>
      <TD width="1%">&nbsp;</TD>
  </TR>
  
  <!-- End Table Head -->
  <!-- Begin Table Body -->
  <TR valign="bottom">
      <TD width="1%" style="border-top: 2px solid #000000">&nbsp;</TD>
                      <TD align="center" style="border-top: 2px solid #000000"><DIV style="margin-left:15px; text-indent:-15px">Common Stock,
  $0.001 par value
  per share</DIV></TD>
      <TD style="border-right: 2px solid #000000; border-top: 2px solid #000000">&nbsp;</TD>
      <TD style="border-top: 2px solid #000000">&nbsp;</TD>
      <TD nowrap colspan="3" align="center" style="border-top: 2px solid #000000">4,135,009 shares(2)</TD>
      <TD style="border-right: 2px solid #000000; border-top: 2px solid #000000">&nbsp;</TD>
      <TD style="border-top: 2px solid #000000">&nbsp;</TD>
  
  <TD nowrap align="center" style="border-top: 2px solid #000000" colspan="3">$12.95(3)</TD>
      <TD style="border-right: 2px solid #000000; border-top: 2px solid #000000">&nbsp;</TD>
      <TD style="border-top: 2px solid #000000">&nbsp;</TD>
  
  <TD nowrap align="center" style="border-top: 2px solid #000000" colspan="3">$53,548,366.55(3)</TD>
      <TD style="border-right: 2px solid #000000; border-top: 2px solid #000000">&nbsp;</TD>
      <TD style="border-top: 2px solid #000000">&nbsp;</TD>
  
  <TD align="center" style="border-top: 2px solid #000000" colspan="2">$5,729.68</TD>
  </TR>
  <TR style="font-size: 1px">
  
      <TD width="1%">&nbsp;</TD>
      <TD nowrap align="center">&nbsp;</TD>
      <TD style="border-right: 2px solid #000000">&nbsp;</TD>
      <TD>&nbsp;</TD>
      <TD nowrap align="center" colspan="2">&nbsp;</TD>
      <TD>&nbsp;</TD>
      <TD style="border-right: 2px solid #000000">&nbsp;</TD>
      <TD>&nbsp;</TD>
      <TD nowrap align="center" colspan="2">&nbsp;</TD>
      <TD>&nbsp;</TD>
      <TD style="border-right: 2px solid #000000">&nbsp;</TD>
      <TD>&nbsp;</TD>
      <TD nowrap align="center" colspan="2">&nbsp;</TD>
      <TD>&nbsp;</TD>
      <TD style="border-right: 2px solid #000000">&nbsp;</TD>
      <TD>&nbsp;</TD>
      <TD nowrap align="center" colspan="2">&nbsp;</TD>
      <TD>&nbsp;</TD>
      <TD width="1%">&nbsp;</TD>
  </TR>
  <TR style="font-size: 1px" valign="bottom">
      <TD nowrap align="left" colspan="21" style="border-top: 3px solid #000000">&nbsp;</TD>
  </TR>
  
  <!-- End Table Body -->
  </TABLE>
  </DIV>
  
  <DIV style="margin-top: 6pt">
  <TABLE width="100%" border="0" cellpadding="0" cellspacing="0" style="font-size: 10pt">
  
  <TR valign="top" style="font-size: 10pt; color: #000000; background: transparent">
      <TD width="1%" nowrap align="left">(1)</TD>
      <TD width="1%">&nbsp;</TD>
      <TD>In accordance with Rule&nbsp;416 under the Securities Act of 1933, as amended, this registration
  statement shall be deemed to cover any additional securities that may from time to time be
  offered or issued to prevent dilution resulting from stock splits, stock dividends or similar
  transactions.</TD>
  </TR>
  
  </TABLE>
  </DIV>
  
  <DIV style="margin-top: 6pt">
  <TABLE width="100%" border="0" cellpadding="0" cellspacing="0" style="font-size: 10pt">
  
  <TR valign="top" style="font-size: 10pt; color: #000000; background: transparent">
      <TD width="1%" nowrap align="left">(2)</TD>
      <TD width="1%">&nbsp;</TD>
      <TD>Consists of (i)&nbsp;4,085,009 shares issuable under the 1999 Stock Option and Grant Plan and/or
  the 2005 Stock Incentive Plan and (ii)&nbsp;50,000 shares issuable under the 2005 Employee Stock
  Purchase Plan.</TD>
  </TR>
  
  </TABLE>
  </DIV>
  
  <DIV style="margin-top: 6pt">
  <TABLE width="100%" border="0" cellpadding="0" cellspacing="0" style="font-size: 10pt">
  
  <TR valign="top" style="font-size: 10pt; color: #000000; background: transparent">
      <TD width="1%" nowrap align="left">(3)</TD>
      <TD width="1%">&nbsp;</TD>
      <TD>Estimated solely for the purpose of calculating the registration fee pursuant to Rules 457(c)
  and 457(h) of the Securities Act of 1933, as amended, and based upon the average of the high
  and low prices of the Registrant&#146;s Common Stock as reported on the Nasdaq National Market on
  December&nbsp;8, 2005.</TD>
  </TR>
  
  </TABLE>
  </DIV>
  
  <DIV style="width: 100%; border-bottom: 1pt solid black; margin-top: 10pt; font-size: 1pt">&nbsp;</DIV>
  <DIV style="width: 100%; border-bottom: 2pt solid black; font-size: 1pt">&nbsp;</DIV>
  
  
  
  
  
  <P align="center" style="font-size: 10pt">&nbsp;
  </DIV>
  
  <!-- PAGEBREAK -->
  <P><HR noshade><P>
  
  <DIV style="font-family: 'Times New Roman',Times,serif">
  
  <!-- TOC -->
  <A name="toc"><DIV align="CENTER" style="page-break-before:always"><U><B>TABLE OF CONTENTS</B></U></DIV></A>
  
  <P><CENTER>
  <TABLE border="0" width="90%" cellpadding="0" cellspacing="0">
  <TR>
  	<TD width="3%"></TD>
  	<TD width="3%"></TD>
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  	<TD width="3%"></TD>
  	<TD width="76%"></TD>
  </TR>
  <TR><TD colspan="9"><A HREF="#000"> PART I</A></TD></TR>
  <TR><TD></TD><TD colspan="8"><A HREF="#001"> Item&nbsp;1. Plan Information</A></TD></TR>
  <TR><TD></TD><TD colspan="8"><A HREF="#002"> Item&nbsp;2. Registrant Information and Employee Plan Annual Information</A></TD></TR>
  <TR><TD colspan="9"><A HREF="#003"> PART II</A></TD></TR>
  <TR><TD></TD><TD colspan="8"><A HREF="#004"> Item&nbsp;3. Incorporation of Documents by Reference</A></TD></TR>
  <TR><TD></TD><TD colspan="8"><A HREF="#005"> Item&nbsp;4. Description of Securities</A></TD></TR>
  <TR><TD></TD><TD colspan="8"><A HREF="#006"> Item&nbsp;5. Interests of Named Experts and Counsel</A></TD></TR>
  <TR><TD></TD><TD colspan="8"><A HREF="#007"> Item&nbsp;6. Indemnification of Directors and Officers</A></TD></TR>
  <TR><TD></TD><TD colspan="8"><A HREF="#008"> Item&nbsp;7. Exemption from Registration Claimed</A></TD></TR>
  <TR><TD></TD><TD colspan="8"><A HREF="#009"> Item&nbsp;8. Exhibits</A></TD></TR>
  <TR><TD></TD><TD colspan="8"><A HREF="#010">Item&nbsp;9. Undertakings</A></TD></TR>
  <TR><TD colspan="9"><A HREF="#011"> SIGNATURES</A></TD></TR>
  <TR><TD colspan="9"><A HREF="#012">INDEX TO EXHIBITS</A></TD></TR>
  <TR><TD colspan="9"><A HREF="b58101nmexv5.htm">EX-5 OPINION OF WILMER CUTLER PICKERING HALE AND DORR LLP</A></TD></TR>
  <TR><TD colspan="9"><A HREF="b58101nmexv23w2.htm">EX-23.2 CONSENT OF ERNST & YOUNG LLP</A></TD></TR>
  </TABLE>
  </CENTER>
  <!-- /TOC -->
  <P><HR noshade><P>
  <H5 align="left" style="page-break-before:always"><A HREF="#toc">Table of Contents</A></H5><P>
  
  <!-- link1 " PART I" -->
  <DIV align="left"><A NAME="000"></A></DIV>
  
  <DIV align="center" style="font-size: 10pt; margin-top: 18pt"><B>PART I</B>
  </DIV>
  
  <DIV align="center" style="font-size: 10pt"><B>INFORMATION REQUIRED IN THE SECTION 10(a) PROSPECTUS</B></DIV>
  
  
  <!-- link2 " Item&nbsp;1. Plan Information" -->
  <DIV align="left"><A NAME="001"></A></DIV>
  
  <DIV align="left" style="font-size: 10pt; margin-top: 6pt">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<B>Item&nbsp;1. Plan Information.</B>
  </DIV>
  
  <DIV align="left" style="font-size: 10pt; margin-top: 6pt">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;The information required by Item&nbsp;1 is included in documents sent or given to participants in
  the plans covered by this registration statement pursuant to Rule&nbsp;428(b)(1) of the Securities Act
  of 1933, as amended (the &#147;Securities Act&#148;).
  </DIV>
  <!-- link2 " Item&nbsp;2. Registrant Information and Employee Plan Annual Information" -->
  <DIV align="left"><A NAME="002"></A></DIV>
  
  <DIV align="left" style="font-size: 10pt; margin-top: 6pt">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<B>Item&nbsp;2. Registrant Information and Employee Plan Annual Information.</B>
  </DIV>
  
  <DIV align="left" style="font-size: 10pt; margin-top: 6pt">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;The written statement required by Item&nbsp;2 is included in documents sent or given to
  participants in the plans covered by this registration statement pursuant to Rule&nbsp;428(b)(1) of the
  Securities Act.
  </DIV>
  <!-- link1 " PART II" -->
  <DIV align="left"><A NAME="003"></A></DIV>
  
  <DIV align="center" style="font-size: 10pt; margin-top: 18pt"><B>PART II</B>
  </DIV>
  
  <DIV align="center" style="font-size: 10pt"><B>INFORMATION REQUIRED IN THE REGISTRATION STATEMENT</B></DIV>
  
  
  <!-- link2 " Item&nbsp;3. Incorporation of Documents by Reference" -->
  <DIV align="left"><A NAME="004"></A></DIV>
  
  <DIV align="left" style="font-size: 10pt; margin-top: 6pt">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<B>Item&nbsp;3. Incorporation of Documents by Reference.</B>
  </DIV>
  
  <DIV align="left" style="font-size: 10pt; margin-top: 6pt">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;The registrant is subject to the informational and reporting requirements of Sections&nbsp;13(a),
  14, and 15(d) of the Securities Exchange Act of 1934, as amended (the &#147;Exchange Act&#148;), and in
  accordance therewith files reports, proxy statements and other information with the Securities and
  Exchange Commission (the &#147;Commission&#148;). The following documents, which are on file with the
  Commission, are incorporated in this registration statement by reference:
  </DIV>
  
  <DIV align="left" style="font-size: 10pt; margin-top: 6pt">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(a)&nbsp;The registrant&#146;s latest annual report filed pursuant to Section 13(a) or 15(d) of the
  Exchange Act or the latest prospectus filed pursuant to Rule 424(b) under the Securities Act that
  contains audited financial statements for the registrant&#146;s latest fiscal year for which such
  statements have been filed.
  </DIV>
  
  <DIV align="left" style="font-size: 10pt; margin-top: 6pt">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(b)&nbsp;All other reports filed pursuant to Section 13(a) or 15(d) of the Exchange Act since the
  end of the fiscal year covered by the document referred to in (a)&nbsp;above.
  </DIV>
  
  <DIV align="left" style="font-size: 10pt; margin-top: 6pt">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(c)&nbsp;The description of the securities contained in the registrant&#146;s registration statement on
  Form 8-A filed under the Exchange Act, including any amendment or report filed for the purpose of
  updating such description.
  </DIV>
  
  <DIV align="left" style="font-size: 10pt; margin-top: 6pt">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;All documents subsequently filed by the registrant pursuant to Sections&nbsp;13(a), 13(c), 14 and
  15(d) of the Exchange Act, prior to the filing of a post-effective amendment which indicates that
  all securities offered hereby have been sold or which deregisters all securities then remaining
  unsold, shall be deemed to be incorporated by reference in this registration statement and to be
  part hereof from the date of the filing of such documents. Any statement contained in a document
  incorporated or deemed to be incorporated by reference herein shall be deemed to be modified or
  superseded for the purposes of this registration statement to the extent that a statement contained
  herein or in any other subsequently filed document which also is or is deemed to be incorporated by
  reference herein modifies or supersedes such statement. Any statement so modified or superseded
  shall not be deemed, except as so modified or superseded, to constitute a part of this registration
  statement.
  </DIV>
  <!-- link2 " Item&nbsp;4. Description of Securities" -->
  <DIV align="left"><A NAME="005"></A></DIV>
  
  <DIV align="left" style="font-size: 10pt; margin-top: 6pt">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<B>Item&nbsp;4. Description of Securities.</B>
  </DIV>
  
  <DIV align="left" style="font-size: 10pt; margin-top: 6pt">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Not applicable.
  </DIV>
  
  <P align="center" style="font-size: 10pt">- 1 -
  </DIV>
  
  <!-- PAGEBREAK -->
  <P><HR noshade><P>
  <H5 align="left" style="page-break-before:always"><A HREF="#toc">Table of Contents</A></H5><P>
  
  <DIV style="font-family: 'Times New Roman',Times,serif">
  <!-- link2 " Item&nbsp;5. Interests of Named Experts and Counsel" -->
  <DIV align="left"><A NAME="006"></A></DIV>
  
  <DIV align="left" style="font-size: 10pt; margin-top: 6pt">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<B>Item&nbsp;5. Interests of Named Experts and Counsel.</B>
  </DIV>
  
  <DIV align="left" style="font-size: 10pt; margin-top: 6pt">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Wilmer Cutler Pickering Hale and Dorr LLP has opined as to the legality of the securities
  being offered by this registration statement.
  </DIV>
  <!-- link2 " Item&nbsp;6. Indemnification of Directors and Officers" -->
  <DIV align="left"><A NAME="007"></A></DIV>
  
  <DIV align="left" style="font-size: 10pt; margin-top: 6pt">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<B>Item&nbsp;6. Indemnification of Directors and Officers.</B>
  </DIV>
  
  <DIV align="left" style="font-size: 10pt; margin-top: 6pt">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Section&nbsp;102 of the Delaware General Corporation Law allows a corporation to eliminate the
  personal liability of directors of a corporation to the corporation or its stockholders for
  monetary damages for a breach of fiduciary duty as a director, except where the director breached
  his duty of loyalty, failed to act in good faith, engaged in intentional misconduct or knowingly
  violated a law, authorized the payment of a dividend or approved a stock repurchase in violation of
  Delaware corporate law or obtained an improper personal benefit. The registrant has included such a
  provision in its Restated Certificate of Incorporation.
  </DIV>
  
  <DIV align="left" style="font-size: 10pt; margin-top: 6pt">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Section&nbsp;145 of the General Corporation Law of Delaware provides that a corporation has the
  power to indemnify a director, officer, employee or agent of the corporation and certain other
  persons serving at the request of the corporation in related capacities against amounts paid and
  expenses incurred in connection with an action or proceeding to which he is or is threatened to be
  made a party by reason of such position, if such person shall have acted in good faith and in a
  manner he reasonably believed to be in or not opposed to the best interests of the corporation,
  and, in any criminal proceeding, if such person had no reasonable cause to believe his conduct was
  unlawful; provided that, in the case of actions brought by or in the right of the corporation, no
  indemnification shall be made with respect to any matter as to which such person shall have been
  adjudged to be liable to the corporation unless and only to the extent that the adjudicating court
  determines that such indemnification is proper under the circumstances.
  </DIV>
  
  <DIV align="left" style="font-size: 10pt; margin-top: 6pt">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;The registrant&#146;s Restated Certificate of Incorporation includes a provision that eliminates
  the personal liability of its directors for monetary damages for breach of fiduciary duty as a
  director, except for liability:
  </DIV>
  
  <DIV style="margin-top: 6pt">
  <TABLE width="100%" border="0" cellpadding="0" cellspacing="0" style="font-size: 10pt">
  
  <TR valign="top" style="font-size: 10pt; color: #000000; background: transparent">
      <TD width="2%" style="background: transparent">&nbsp;</TD>
      <TD width="3%" nowrap align="left"><B>&#149;</B></TD>
      <TD width="1%">&nbsp;</TD>
      <TD>for any breach of the director&#146;s duty of loyalty to the registrant or its
  stockholders;</TD>
  </TR>
  
  <TR>
      <TD style="font-size: 6pt">&nbsp;</TD>
  </TR><TR valign="top" style="font-size: 10pt; color: #000000; background: transparent">
      <TD width="2%" style="background: transparent">&nbsp;</TD>
      <TD width="3%" nowrap align="left"><B>&#149;</B></TD>
      <TD width="1%">&nbsp;</TD>
      <TD>for acts or omissions not in good faith or that involve intentional misconduct or a
  knowing violation of law;</TD>
  </TR>
  
  <TR>
      <TD style="font-size: 6pt">&nbsp;</TD>
  </TR><TR valign="top" style="font-size: 10pt; color: #000000; background: transparent">
      <TD width="2%" style="background: transparent">&nbsp;</TD>
      <TD width="3%" nowrap align="left"><B>&#149;</B></TD>
      <TD width="1%">&nbsp;</TD>
      <TD>under Section&nbsp;174 of the Delaware General Corporation Law regarding unlawful
  dividends and stock purchases; or</TD>
  </TR>
  
  <TR>
      <TD style="font-size: 6pt">&nbsp;</TD>
  </TR><TR valign="top" style="font-size: 10pt; color: #000000; background: transparent">
      <TD width="2%" style="background: transparent">&nbsp;</TD>
      <TD width="3%" nowrap align="left"><B>&#149;</B></TD>
      <TD width="1%">&nbsp;</TD>
      <TD>for any transaction from which the director derived an improper personal benefit.</TD>
  </TR>
  
  </TABLE>
  </DIV>
  <DIV align="left" style="font-size: 10pt; margin-top: 6pt">These provisions are permitted under Delaware law. The registrant&#146;s Amended and Restated Bylaws
  provide that:
  </DIV>
  
  
  <DIV style="margin-top: 6pt">
  <TABLE width="100%" border="0" cellpadding="0" cellspacing="0" style="font-size: 10pt">
  
  <TR valign="top" style="font-size: 10pt; color: #000000; background: transparent">
      <TD width="2%" style="background: transparent">&nbsp;</TD>
      <TD width="3%" nowrap align="left"><B>&#149;</B></TD>
      <TD width="1%">&nbsp;</TD>
      <TD>it must indemnify its directors and officers to the fullest extent permitted by
  Delaware law;</TD>
  </TR>
  
  <TR>
      <TD style="font-size: 6pt">&nbsp;</TD>
  </TR><TR valign="top" style="font-size: 10pt; color: #000000; background: transparent">
      <TD width="2%" style="background: transparent">&nbsp;</TD>
      <TD width="3%" nowrap align="left"><B>&#149;</B></TD>
      <TD width="1%">&nbsp;</TD>
      <TD>it may indemnify its other employees and agents to the same extent that it
  indemnified its officers and directors, unless otherwise determined by its Board of
  Directors; and</TD>
  </TR>
  
  <TR>
      <TD style="font-size: 6pt">&nbsp;</TD>
  </TR><TR valign="top" style="font-size: 10pt; color: #000000; background: transparent">
      <TD width="2%" style="background: transparent">&nbsp;</TD>
      <TD width="3%" nowrap align="left"><B>&#149;</B></TD>
      <TD width="1%">&nbsp;</TD>
      <TD>it must advance expenses, as incurred, to its directors and executive officers in
  connection with a legal proceeding to the fullest extent permitted by Delaware law.</TD>
  </TR>
  
  </TABLE>
  </DIV>
  
  <DIV align="left" style="font-size: 10pt; margin-top: 6pt">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;The indemnification provisions contained in the registrant&#146;s Restated Certificate of
  Incorporation and Amended and Restated Bylaws are not exclusive of any other rights to which a
  person may be entitled by law, agreement, vote of stockholders or disinterested directors or
  otherwise.
  </DIV>
  
  <P align="center" style="font-size: 10pt">- 2 -
  </DIV>
  
  <!-- PAGEBREAK -->
  <P><HR noshade><P>
  <H5 align="left" style="page-break-before:always"><A HREF="#toc">Table of Contents</A></H5><P>
  
  <DIV style="font-family: 'Times New Roman',Times,serif">
  
  <DIV align="left" style="font-size: 10pt; margin-top: 6pt">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;In addition to the indemnification provided for in the Registrant&#146;s restated certificate of
  incorporation and restated bylaws, the registrant has entered into indemnification agreements with
  each of its directors and executive officers. Each indemnification agreement provides that it will
  indemnify the director or executive officer to the fullest extent permitted by law for claims
  arising in his or her capacity as a director, officer, employee or agent of the Registrant,
  provided that he or she acted in good faith and in a manner that he or she reasonably believed to
  be in, or not opposed to, the Registrant&#146;s best interests and, with respect to any criminal
  proceeding, had no reasonable cause to believe that his or her conduct was unlawful. If the claim
  is brought by or on behalf of the Registrant, the Registrant will not be obligated to indemnify the
  director or executive officer if he or she is found liable to the Registrant, unless the court
  determines that, despite the adjudication of liability, in view of all the circumstances of the
  case the director or executive officer is fairly and reasonably entitled to be indemnified. In the
  event that the Registrant does not assume the defense of a claim against a director or executive
  officer, the Registrant is required to advance his or her expenses in connection with his or her
  defense, provided that he or she undertakes to repay all amounts advanced if it is ultimately
  determined that he or she is not entitled to be indemnified by the Registrant.
  </DIV>
  
  <DIV align="left" style="font-size: 10pt; margin-top: 6pt">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;The registrant also maintains insurance on behalf of its directors and executive officers
  insuring them against any liability asserted against them in their capacities as directors or
  officers or arising out of such status.
  </DIV>
  <!-- link2 " Item&nbsp;7. Exemption from Registration Claimed" -->
  <DIV align="left"><A NAME="008"></A></DIV>
  
  <DIV align="left" style="font-size: 10pt; margin-top: 6pt">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<B>Item&nbsp;7. Exemption from Registration Claimed.</B>
  </DIV>
  
  <DIV align="left" style="font-size: 10pt; margin-top: 6pt">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Not applicable.
  </DIV>
  <!-- link2 " Item&nbsp;8. Exhibits" -->
  <DIV align="left"><A NAME="009"></A></DIV>
  
  <DIV align="left" style="font-size: 10pt; margin-top: 6pt">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<B>Item&nbsp;8. Exhibits.</B>
  </DIV>
  
  <DIV align="left" style="font-size: 10pt; margin-top: 6pt">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;The Exhibit&nbsp;Index immediately preceding the exhibits is incorporated herein by reference.
  </DIV>
  <!-- link2 "Item&nbsp;9. Undertakings" -->
  <DIV align="left"><A NAME="010"></A></DIV>
  
  <DIV align="left" style="font-size: 10pt; margin-top: 6pt">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<B>Item&nbsp;9. Undertakings.</B>
  </DIV>
  
  <DIV align="left" style="font-size: 10pt; margin-top: 6pt">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;1.&nbsp;<U><I>Item&nbsp;</I><I>512(a)</I><I> of Regulation&nbsp;S-K</I></U>. The undersigned registrant hereby undertakes:
  </DIV>
  
  
  <DIV align="left" style="font-size: 10pt; margin-top: 6pt; margin-left: 3%">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(1) To file, during any period in which offers or sales are being made, a
  post-effective amendment to this registration statement:
  </DIV>
  
  
  <DIV align="left" style="font-size: 10pt; margin-top: 6pt; margin-left: 3%">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(i) To include any prospectus required by Section&nbsp;10(a)(3) of the Securities Act;
  </DIV>
  
  
  <DIV align="left" style="font-size: 10pt; margin-top: 6pt; margin-left: 3%">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(ii) To reflect in the prospectus any facts or events arising after the effective date
  of the registration statement (or the most recent post-effective amendment thereof) which,
  individually or in the aggregate, represent a fundamental change in the information set
  forth in the registration statement; and
  </DIV>
  
  
  <DIV align="left" style="font-size: 10pt; margin-top: 6pt; margin-left: 3%">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(iii) To include any material information with respect to the plan of distribution not
  previously disclosed in the registration statement or any material change to such
  information in the registration statement;
  </DIV>
  
  
  <DIV align="left" style="font-size: 10pt; margin-top: 6pt; margin-left: 3%"><I>provided, however, </I>that paragraphs (i)&nbsp;and (ii)&nbsp;do not apply if the information required to
  be included in a post-effective amendment by those paragraphs is contained in periodic
  reports filed with or furnished to the Commission by the registrant pursuant to Section&nbsp;13
  or Section 15(d) of the Exchange Act that are incorporated by reference in the registration
  statement.
  </DIV>
  
  <P align="center" style="font-size: 10pt">- 3 -
  </DIV>
  
  <!-- PAGEBREAK -->
  <P><HR noshade><P>
  <H5 align="left" style="page-break-before:always"><A HREF="#toc">Table of Contents</A></H5><P>
  
  <DIV style="font-family: 'Times New Roman',Times,serif">
  
  
  <DIV align="left" style="font-size: 10pt; margin-top: 6pt; margin-left: 3%">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(2) That, for the purpose of determining any liability under the Securities Act, each
  such post-effective amendment shall be deemed to be a new registration statement relating to
  the securities offered therein, and the offering of such securities at that time shall be
  deemed to be the initial <I>bona fide </I>offering thereof.
  </DIV>
  
  
  <DIV align="left" style="font-size: 10pt; margin-top: 6pt; margin-left: 3%">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(3) To remove from registration by means of a post-effective amendment any of the
  securities being registered which remain unsold at the termination of the offering.
  </DIV>
  
  <DIV align="left" style="font-size: 10pt; margin-top: 6pt">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;2.&nbsp;<U><I>Item&nbsp;</I><I>512(b)</I><I> of Regulation&nbsp;S-K</I></U>. The undersigned registrant hereby undertakes that,
  for purposes of determining any liability under the Securities Act, each filing of the registrant&#146;s
  annual report pursuant to Section 13(a) or Section 15(d) of the Exchange Act that is incorporated
  by reference in the registration statement shall be deemed to be a new registration statement
  relating to the securities offered therein, and the offering of such securities at that time shall
  be deemed to be the initial <I>bona fide </I>offering thereof.
  </DIV>
  
  <DIV align="left" style="font-size: 10pt; margin-top: 6pt">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;3.&nbsp;<U><I>Item&nbsp;</I><I>512(h)</I><I> of Regulation&nbsp;S-K</I></U>. Insofar as indemnification for liabilities arising
  under the Securities Act may be permitted to directors, officers and controlling persons of the
  registrant pursuant to the foregoing provisions, or otherwise, the registrant has been advised that
  in the opinion of the Securities and Exchange Commission such indemnification is against public
  policy as expressed in the Securities Act and is, therefore, unenforceable. In the event that a
  claim for indemnification against such liabilities (other than the payment by the registrant of
  expenses incurred or paid by a director, officer or controlling person of the registrant in the
  successful defense of any action, suit or proceeding) is asserted by such director, officer or
  controlling person in connection with the securities being registered, the registrant will, unless
  in the opinion of its counsel the matter has been settled by controlling precedent, submit to a
  court of appropriate jurisdiction the question whether such indemnification by it is against public
  policy as expressed in the Securities Act and will be governed by the final adjudication of such
  issue.
  </DIV>
  
  <P align="center" style="font-size: 10pt">- 4 -
  </DIV>
  
  <!-- PAGEBREAK -->
  <P><HR noshade><P>
  <H5 align="left" style="page-break-before:always"><A HREF="#toc">Table of Contents</A></H5><P>
  
  <DIV style="font-family: 'Times New Roman',Times,serif">
  <!-- link1 " SIGNATURES" -->
  <DIV align="left"><A NAME="011"></A></DIV>
  
  <DIV align="center" style="font-size: 10pt; margin-top: 18pt"><B>SIGNATURES</B>
  </DIV>
  
  
  <DIV align="left" style="font-size: 10pt; margin-top: 6pt">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Pursuant to the requirements of the Securities Act of 1933, the registrant certifies that it
  has reasonable grounds to believe that it meets all of the requirements for filing on Form S-8 and
  has duly caused this registration statement to be signed on its behalf by the undersigned,
  thereunto duly authorized, in Lawrence, Massachusetts on this
  9th&nbsp;day of December, 2005.
  </DIV>
  
  <TABLE width="100%" border="0" cellspacing="0" cellpadding="0" style="font-size: 10pt">
  <TR>
      <TD width="48%">&nbsp;</TD>
      <TD width="1%">&nbsp;</TD>
      <TD width="1%">&nbsp;</TD>
      <TD width="35%">&nbsp;</TD>
      <TD width="15%">&nbsp;</TD>
  </TR>
  <TR>
      <TD valign="top" align="left">&nbsp;</TD>
      <TD colspan="3" align="left">NXSTAGE MEDICAL, INC.<BR>
  &nbsp;</TD>
      <TD>&nbsp;</TD>
  </TR><TR>
      <TD align="left">&nbsp;</TD>
      <TD valign="top">By:&nbsp;&nbsp;</TD>
  
  <TD colspan="2" style="border-bottom: 1px solid #000000" align="left">/s/
  Jeffrey H. Burbank</TD>
      <TD>&nbsp;</TD>
  </TR><TR>
      <TD align="left">&nbsp;</TD>
      <TD>&nbsp;</TD>
      <TD valign="top">Name:&nbsp;&nbsp;</TD>
      <TD align="left">Jeffrey H. Burbank</TD>
      <TD>&nbsp;</TD>
  </TR><TR>
      <TD align="left">&nbsp;</TD>
      <TD>&nbsp;</TD>
      <TD valign="top">Title:&nbsp;&nbsp;</TD>
      <TD align="left">President and Chief Executive Officer</TD>
      <TD>&nbsp;</TD>
  </TR>
  </TABLE>
  
  <DIV align="center" style="font-size: 10pt; margin-top: 18pt"><B>POWER OF ATTORNEY AND SIGNATURES</B>
  </DIV>
  
  
  
  <DIV align="left" style="font-size: 10pt; margin-top: 6pt">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;We, the undersigned officers and directors of NxStage Medical, Inc., hereby severally
  constitute and appoint Jeffrey H. Burbank, David N. Gill and Winifred L. Swan, and each of them
  singly, our true and lawful attorneys with full power to them, and each of them singly, to sign for
  us and in our names in the capacities indicated below, the registration statement on Form S-8 filed
  herewith and any and all subsequent amendments to said registration statement, and generally to do
  all such things in our names and on our behalf in our capacities as officers and directors to
  enable NxStage Medical, Inc. to comply with the provisions of the Securities Act of 1933, as
  amended, and all requirements of the Securities and Exchange Commission, hereby ratifying and
  confirming our signatures as they may be signed by our said attorneys, or any of them, to said
  registration statement and any and all amendments thereto.
  </DIV>
  
  <DIV align="left" style="font-size: 10pt; margin-top: 6pt">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Pursuant to the requirements of the Securities Act of 1933, this registration statement has
  been signed by the following persons in the capacities and on the dates indicated.
  </DIV>
  
  <DIV align="center">
  <TABLE style="font-size: 10pt" cellspacing="0" border="0" cellpadding="0" width="100%">
  <!-- Begin Table Head -->
  <TR valign="bottom">
      <TD width="30%">&nbsp;</TD>
      <TD width="5%">&nbsp;</TD>
      <TD width="30%">&nbsp;</TD>
      <TD width="5%">&nbsp;</TD>
      <TD width="30%">&nbsp;</TD>
  </TR>
  
  <!-- End Table Head -->
  <!-- Begin Table Body -->
  <TR valign="bottom">
      <TD align="center" valign="top"><DIV style="margin-left:0px; text-indent:-0px"><B>Signature</B>
  </DIV></TD>
      <TD>&nbsp;</TD>
      <TD align="center" valign="top"><B>Title</B>
  </TD>
      <TD>&nbsp;</TD>
      <TD align="center" valign="top"><B>Date</B></TD>
  </TR>
  <TR style="font-size: 1px">
      <TD valign="top" style="border-top: 1px solid #000000"><DIV style="margin-left:0px; text-indent:-0px">&nbsp;
  </DIV></TD>
      <TD>&nbsp;</TD>
      <TD align="left" valign="top" style="border-top: 1px solid #000000">&nbsp;
  </TD>
      <TD>&nbsp;</TD>
      <TD align="center" valign="top" style="border-top: 1px solid #000000">&nbsp;</TD>
  </TR>
  <TR valign="bottom"><!-- Blank Space -->
  
  <TD valign="top"><DIV style="margin-left:0px; text-indent:-0px">&nbsp;</DIV></TD>
      <TD>&nbsp;</TD>
      <TD align="left" valign="top">&nbsp;</TD>
      <TD>&nbsp;</TD>
      <TD align="center" valign="top">&nbsp;</TD>
  </TR>
  <TR valign="bottom">
      <TD valign="top"><DIV style="margin-left:0px; text-indent:-0px">/s/ Jeffrey H. Burbank
  </DIV></TD>
      <TD>&nbsp;</TD>
      <TD align="left" valign="top">Chief Executive Officer
  </TD>
      <TD>&nbsp;</TD>
      <TD align="center" valign="top">December&nbsp;9, 2005</TD>
  </TR>
  <TR valign="bottom">
      <TD valign="top"><DIV style="margin-left:0px; text-indent:-0px"><DIV style="border-bottom: 1px solid #000000; font-size: 1px">&nbsp;</DIV>
  Jeffrey H. Burbank
  </DIV></TD>
      <TD>&nbsp;</TD>
      <TD align="left" valign="top">(Principal executive officer)</TD>
      <TD>&nbsp;</TD>
      <TD align="center" valign="top">&nbsp;</TD>
  </TR>
  <TR valign="bottom"><!-- Blank Space -->
      <TD valign="top"><DIV style="margin-left:0px; text-indent:-0px">&nbsp;</DIV></TD>
      <TD>&nbsp;</TD>
      <TD align="left" valign="top">&nbsp;</TD>
      <TD>&nbsp;</TD>
      <TD align="center" valign="top">&nbsp;</TD>
  </TR>
  <TR valign="bottom">
  
  <TD valign="top"><DIV style="margin-left:0px; text-indent:-0px">/s/
  David N. Gill
  </DIV></TD>
      <TD>&nbsp;</TD>
      <TD align="left" valign="top">Chief Financial Officer
  </TD>
      <TD>&nbsp;</TD>
      <TD align="center" valign="top">December 9, 2005</TD>
  </TR>
  <TR valign="bottom">
  
  <TD valign="top"><DIV style="margin-left:0px; text-indent:-0px"><DIV style="border-bottom: 1px solid #000000; font-size: 1px">&nbsp;</DIV>
  David N. Gill
  </DIV></TD>
      <TD>&nbsp;</TD>
      <TD align="left" valign="top" nowrap>(Principal financial and
  accounting officer)</TD>
      <TD>&nbsp;</TD>
      <TD align="center" valign="top">&nbsp;</TD>
  </TR>
  <TR valign="bottom"><!-- Blank Space -->
      <TD valign="top"><DIV style="margin-left:0px; text-indent:-0px">&nbsp;</DIV></TD>
      <TD>&nbsp;</TD>
      <TD align="left" valign="top">&nbsp;</TD>
      <TD>&nbsp;</TD>
      <TD align="center" valign="top">&nbsp;</TD>
  </TR>
  <TR valign="bottom">
  
  <TD valign="top"><DIV style="margin-left:0px; text-indent:-0px">/s/ Philippe O. Chambon, M.D., Ph.D.
  </DIV></TD>
      <TD>&nbsp;</TD>
      <TD align="left" valign="top">Director
  </TD>
      <TD>&nbsp;</TD>
      <TD align="center" valign="top">December 9, 2005</TD>
  </TR>
  <TR valign="bottom">
  
  <TD valign="top"><DIV style="margin-left:0px; text-indent:-0px"><DIV style="border-bottom: 1px solid #000000; font-size: 1px">&nbsp;</DIV>
  Philippe O. Chambon, M.D., Ph.D.</DIV></TD>
      <TD>&nbsp;</TD>
      <TD align="left" valign="top">&nbsp;</TD>
      <TD>&nbsp;</TD>
      <TD align="center" valign="top">&nbsp;</TD>
  </TR>
  <TR valign="bottom"><!-- Blank Space -->
      <TD valign="top"><DIV style="margin-left:0px; text-indent:-0px">&nbsp;</DIV></TD>
      <TD>&nbsp;</TD>
      <TD align="left" valign="top">&nbsp;</TD>
      <TD>&nbsp;</TD>
      <TD align="center" valign="top">&nbsp;</TD>
  </TR>
  <TR valign="bottom">
  
  <TD valign="top"><DIV style="margin-left:0px; text-indent:-0px">/s/ Jean-Francois Formela
  </DIV></TD>
      <TD>&nbsp;</TD>
      <TD align="left" valign="top">Director
  </TD>
      <TD>&nbsp;</TD>
      <TD align="center" valign="top">December 9, 2005</TD>
  </TR>
  <TR valign="bottom" style="font-size: 1px">
      <TD valign="top"><DIV style="margin-left:0px; text-indent:-0px"><DIV style="border-bottom: 1px solid #000000; font-size: 1px">&nbsp;</DIV></DIV></TD>
      <TD>&nbsp;</TD>
      <TD align="left" valign="top">&nbsp;</TD>
      <TD>&nbsp;</TD>
      <TD align="center" valign="top">&nbsp;</TD>
  </TR>
  <TR valign="bottom">
      <TD valign="top"><DIV style="margin-left:0px; text-indent:-0px">Jean-Francois Formela</DIV></TD>
      <TD>&nbsp;</TD>
      <TD align="left" valign="top">&nbsp;</TD>
      <TD>&nbsp;</TD>
      <TD align="center" valign="top">&nbsp;</TD>
  </TR>
  <TR valign="bottom"><!-- Blank Space -->
      <TD valign="top"><DIV style="margin-left:0px; text-indent:-0px">&nbsp;</DIV></TD>
      <TD>&nbsp;</TD>
      <TD align="left" valign="top">&nbsp;</TD>
      <TD>&nbsp;</TD>
      <TD align="center" valign="top">&nbsp;</TD>
  </TR>
  <TR valign="bottom">
  
  <TD valign="top"><DIV style="margin-left:0px; text-indent:-0px">/s/ Daniel A. Giannini
  </DIV></TD>
      <TD>&nbsp;</TD>
      <TD align="left" valign="top">Director
  </TD>
      <TD>&nbsp;</TD>
      <TD align="center" valign="top">December 9, 2005</TD>
  </TR>
  <TR valign="bottom">
      <TD valign="top"><DIV style="margin-left:0px; text-indent:-0px"><DIV style="border-bottom: 1px solid #000000; font-size: 1px">&nbsp;</DIV>
  Daniel A. Giannini</DIV></TD>
      <TD>&nbsp;</TD>
      <TD align="left" valign="top">&nbsp;</TD>
      <TD>&nbsp;</TD>
      <TD align="center" valign="top">&nbsp;</TD>
  </TR>
  <!-- End Table Body -->
  </TABLE>
  </DIV>
  
  
  <P align="center" style="font-size: 10pt">- 5 -
  </DIV>
  
  <!-- PAGEBREAK -->
  <P><HR noshade><P>
  <H5 align="left" style="page-break-before:always"><A HREF="#toc">Table of Contents</A></H5><P>
  
  <DIV style="font-family: 'Times New Roman',Times,serif">
  
  <DIV align="center">
  <TABLE style="font-size: 10pt" cellspacing="0" border="0" cellpadding="0" width="100%">
  <!-- Begin Table Head -->
  <TR valign="bottom">
      <TD width="30%">&nbsp;</TD>
      <TD width="5%">&nbsp;</TD>
      <TD width="30%">&nbsp;</TD>
      <TD width="5%">&nbsp;</TD>
      <TD width="30%">&nbsp;</TD>
  </TR>
  
  <!-- End Table Head -->
  <!-- Begin Table Body -->
  <TR valign="bottom"><TD valign="top"><DIV style="margin-left:0px; text-indent:-0px">/s/ Reid S. Perper
  </DIV></TD>
      <TD>&nbsp;</TD>
      <TD align="left" valign="top">Director
  </TD>
      <TD>&nbsp;</TD>
      <TD align="center" valign="top">December 9, 2005</TD>
  </TR>
  <TR valign="bottom">
      <TD valign="top"><DIV style="margin-left:0px; text-indent:-0px"><DIV style="border-bottom: 1px solid #000000; font-size: 1px">&nbsp;</DIV>
  Reid S. Perper</DIV></TD>
      <TD>&nbsp;</TD>
      <TD align="left" valign="top">&nbsp;</TD>
      <TD>&nbsp;</TD>
      <TD align="center" valign="top">&nbsp;</TD>
  </TR>
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      <TD>&nbsp;</TD>
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      <TD>&nbsp;</TD>
      <TD align="center" valign="top">&nbsp;</TD>
  </TR>
  <TR valign="bottom">
  
  <TD valign="top"><DIV style="margin-left:0px; text-indent:-0px">/s/ Peter P. Phildius
  </DIV></TD>
      <TD>&nbsp;</TD>
      <TD align="left" valign="top">Director
  </TD>
      <TD>&nbsp;</TD>
      <TD align="center" valign="top">December 9, 2005</TD>
  </TR>
  <TR valign="bottom">
      <TD valign="top"><DIV style="margin-left:0px; text-indent:-0px"><DIV style="border-bottom: 1px solid #000000; font-size: 1px">&nbsp;</DIV>
  Peter P. Phildius</DIV></TD>
      <TD>&nbsp;</TD>
      <TD align="left" valign="top">&nbsp;</TD>
      <TD>&nbsp;</TD>
      <TD align="center" valign="top">&nbsp;</TD>
  </TR>
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      <TD valign="top"><DIV style="margin-left:0px; text-indent:-0px">&nbsp;</DIV></TD>
      <TD>&nbsp;</TD>
      <TD align="left" valign="top">&nbsp;</TD>
      <TD>&nbsp;</TD>
      <TD align="center" valign="top">&nbsp;</TD>
  </TR>
  <TR valign="bottom">
  
  <TD valign="top"><DIV style="margin-left:0px; text-indent:-0px">/s/ Craig W. Moore
  </DIV></TD>
      <TD>&nbsp;</TD>
      <TD align="left" valign="top">Director
  </TD>
      <TD>&nbsp;</TD>
      <TD align="center" valign="top">December 9, 2005</TD>
  </TR>
  <TR valign="bottom">
      <TD valign="top"><DIV style="margin-left:0px; text-indent:-0px"><DIV style="border-bottom: 1px solid #000000; font-size: 1px">&nbsp;</DIV>
  Craig W. Moore</DIV></TD>
      <TD>&nbsp;</TD>
      <TD align="left" valign="top">&nbsp;</TD>
      <TD>&nbsp;</TD>
      <TD align="center" valign="top">&nbsp;</TD>
  </TR>
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      <TD valign="top"><DIV style="margin-left:0px; text-indent:-0px">&nbsp;</DIV></TD>
      <TD>&nbsp;</TD>
      <TD align="left" valign="top">&nbsp;</TD>
      <TD>&nbsp;</TD>
      <TD align="center" valign="top">&nbsp;</TD>
  </TR>
  <TR valign="bottom">
  
  <TD valign="top"><DIV style="margin-left:0px; text-indent:-0px">/s/ David S. Utterberg
  </DIV></TD>
      <TD>&nbsp;</TD>
      <TD align="left" valign="top">Director
  </TD>
      <TD>&nbsp;</TD>
      <TD align="center" valign="top">December 9, 2005</TD>
  </TR>
  <TR valign="bottom">
      <TD valign="top"><DIV style="margin-left:0px; text-indent:-0px"><DIV style="border-bottom: 1px solid #000000; font-size: 1px">&nbsp;</DIV>
  David S. Utterberg</DIV></TD>
      <TD>&nbsp;</TD>
      <TD align="left" valign="top">&nbsp;</TD>
      <TD>&nbsp;</TD>
      <TD align="center" valign="top">&nbsp;</TD>
  </TR>
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  <P align="center" style="font-size: 10pt">- 6 -
  </DIV>
  
  <!-- PAGEBREAK -->
  <P><HR noshade><P>
  <H5 align="left" style="page-break-before:always"><A HREF="#toc">Table of Contents</A></H5><P>
  
  <DIV style="font-family: 'Times New Roman',Times,serif">
  
  <!-- link1 "INDEX TO EXHIBITS" -->
  <DIV align="left"><A NAME="012"></A></DIV>
  
  
  <DIV align="center" style="font-size: 10pt; margin-top: 18pt"><B>INDEX TO EXHIBITS</B>
  </DIV>
  
  <DIV align="center">
  <TABLE style="font-size: 10pt" cellspacing="0" border="0" cellpadding="0" width="100%">
  <!-- Begin Table Head -->
  <TR valign="bottom">
      <TD width="5%">&nbsp;</TD>
      <TD width="5%">&nbsp;</TD>
      <TD width="90%">&nbsp;</TD>
  </TR>
  <TR style="font-size: 8pt" valign="bottom">
      <TD nowrap align="left" style="border-bottom: 1px solid #000000">Number</TD>
      <TD>&nbsp;</TD>
      <TD nowrap align="left" style="border-bottom: 1px solid #000000">Description</TD>
  </TR>
  
  <!-- End Table Head -->
  <!-- Begin Table Body -->
  <TR valign="bottom">
      <TD valign="top"><DIV style="margin-left:0px; text-indent:-0px">4.1(1)
  </DIV></TD>
      <TD>&nbsp;</TD>
      <TD align="left" valign="top">Restated Certificate of Incorporation of the Registrant</TD>
  </TR>
  <TR valign="bottom"><!-- Blank Space -->
      <TD valign="top"><DIV style="margin-left:0px; text-indent:-0px">&nbsp;</DIV></TD>
      <TD>&nbsp;</TD>
      <TD align="left" valign="top">&nbsp;</TD>
  </TR>
  <TR valign="bottom">
      <TD valign="top"><DIV style="margin-left:0px; text-indent:-0px">4.2(1)
  </DIV></TD>
      <TD>&nbsp;</TD>
      <TD align="left" valign="top">Restated By-Laws of the Registrant</TD>
  </TR>
  <TR valign="bottom"><!-- Blank Space -->
      <TD valign="top"><DIV style="margin-left:0px; text-indent:-0px">&nbsp;</DIV></TD>
      <TD>&nbsp;</TD>
      <TD align="left" valign="top">&nbsp;</TD>
  </TR>
  <TR valign="bottom">
      <TD valign="top"><DIV style="margin-left:0px; text-indent:-0px">5
  </DIV></TD>
      <TD>&nbsp;</TD>
      <TD align="left" valign="top">Opinion of Wilmer Cutler Pickering Hale and Dorr LLP, counsel to
  the Registrant</TD>
  </TR>
  <TR valign="bottom"><!-- Blank Space -->
      <TD valign="top"><DIV style="margin-left:0px; text-indent:-0px">&nbsp;</DIV></TD>
      <TD>&nbsp;</TD>
      <TD align="left" valign="top">&nbsp;</TD>
  </TR>
  <TR valign="bottom">
      <TD valign="top"><DIV style="margin-left:0px; text-indent:-0px">23.1
  </DIV></TD>
      <TD>&nbsp;</TD>
      <TD align="left" valign="top">Consent of Wilmer Cutler Pickering Hale and Dorr LLP
  (included in Exhibit&nbsp;5)</TD>
  </TR>
  <TR valign="bottom"><!-- Blank Space -->
      <TD valign="top"><DIV style="margin-left:0px; text-indent:-0px">&nbsp;</DIV></TD>
      <TD>&nbsp;</TD>
      <TD align="left" valign="top">&nbsp;</TD>
  </TR>
  <TR valign="bottom">
      <TD valign="top"><DIV style="margin-left:0px; text-indent:-0px">23.2
  </DIV></TD>
      <TD>&nbsp;</TD>
      <TD align="left" valign="top">Consent of Ernst &#038; Young LLP</TD>
  </TR>
  <TR valign="bottom"><!-- Blank Space -->
      <TD valign="top"><DIV style="margin-left:0px; text-indent:-0px">&nbsp;</DIV></TD>
      <TD>&nbsp;</TD>
      <TD align="left" valign="top">&nbsp;</TD>
  </TR>
  <TR valign="bottom">
      <TD valign="top"><DIV style="margin-left:0px; text-indent:-0px">24
  </DIV></TD>
      <TD>&nbsp;</TD>
      <TD align="left" valign="top">Power of attorney (included on the signature pages of this
  registration statement)</TD>
  </TR>
  <!-- End Table Body -->
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      <TD nowrap align="left">(1)</TD>
      <TD>&nbsp;</TD>
      <TD>Previously filed with the Securities and Exchange Commission as an Exhibit to the
  Registrant&#146;s Registration Statement on Form S-1, as amended (File No.&nbsp;333-126711), and
  incorporated herein by reference.</TD>
  </TR>
  
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text: sv8
  Table of Contents
  As
  filed with the Securities and Exchange Commission on December 9, 2005
  Registration No. 333-_____
  SECURITIES AND EXCHANGE COMMISSION
  Washington, D.C. 20549
  FORM S-8
  REGISTRATION STATEMENT UNDER
  THE SECURITIES ACT OF 1933
  NxSTAGE MEDICAL, INC.
  (Exact Name of Registrant as Specified in Its Charter)
  Delaware
  04-3454702
  (State or Other Jurisdiction of Incorporation
  (I.R.S. Employer
  or Organization)
  Identification No.)
  439 South Union Street
  01843
  Lawrence, Massachusetts
  (Address of Principal Executive Offices)
  (Zip Code)
  1999 Stock Option and Grant Plan
  2005 Stock Incentive Plan
  2005 Employee Stock Purchase Plan
  (Full Title of the Plan)
  Jeffrey H. Burbank
  President and Chief Executive Officer
  439 South Union Street
  Lawrence, Massachusetts 01843
  (Name and Address of Agent For Service)
  (978) 687-4700
  (Telephone Number, Including Area Code, of Agent For Service)
  CALCULATION OF REGISTRATION FEE
  Proposed
  Proposed
  Title of
  Maximum
  Maximum
  Securities to be
  Amount to be
  Offering Price Per
  Aggregate
  Amount of
  Registered
  Registered(1)
  Share
  Offering Price
  Registration Fee
  Common Stock,
  $0.001 par value
  per share
  4,135,009 shares(2)
  $12.95(3)
  $53,548,366.55(3)
  $5,729.68
  (1)
  In accordance with Rule 416 under the Securities Act of 1933, as amended, this registration
  statement shall be deemed to cover any additional securities that may from time to time be
  offered or issued to prevent dilution resulting from stock splits, stock dividends or similar
  transactions.
  (2)
  Consists of (i) 4,085,009 shares issuable under the 1999 Stock Option and Grant Plan and/or
  the 2005 Stock Incentive Plan and (ii) 50,000 shares issuable under the 2005 Employee Stock
  Purchase Plan.
  (3)
  Estimated solely for the purpose of calculating the registration fee pursuant to Rules 457(c)
  and 457(h) of the Securities Act of 1933, as amended, and based upon the average of the high
  and low prices of the Registrant's Common Stock as reported on the Nasdaq National Market on
  December 8, 2005.
  TABLE OF CONTENTS
  PART I
  Item 1. Plan Information
  Item 2. Registrant Information and Employee Plan Annual Information
  PART II
  Item 3. Incorporation of Documents by Reference
  Item 4. Description of Securities
  Item 5. Interests of Named Experts and Counsel
  Item 6. Indemnification of Directors and Officers
  Item 7. Exemption from Registration Claimed
  Item 8. Exhibits
  Item 9. Undertakings
  SIGNATURES
  INDEX TO EXHIBITS
  EX-5 OPINION OF WILMER CUTLER PICKERING HALE AND DORR LLP
  EX-23.2 CONSENT OF ERNST & YOUNG LLP
  Table of Contents
  PART I
  INFORMATION REQUIRED IN THE SECTION 10(a) PROSPECTUS
  Item 1. Plan Information.
  The information required by Item 1 is included in documents sent or given to participants in
  the plans covered by this registration statement pursuant to Rule 428(b)(1) of the Securities Act
  of 1933, as amended (the "Securities Act").
  Item 2. Registrant Information and Employee Plan Annual Information.
  The written statement required by Item 2 is included in documents sent or given to
  participants in the plans covered by this registration statement pursuant to Rule 428(b)(1) of the
  Securities Act.
  PART II
  INFORMATION REQUIRED IN THE REGISTRATION STATEMENT
  Item 3. Incorporation of Documents by Reference.
  The registrant is subject to the informational and reporting requirements of Sections 13(a),
  14, and 15(d) of the Securities Exchange Act of 1934, as amended (the "Exchange Act"), and in
  accordance therewith files reports, proxy statements and other information with the Securities and
  Exchange Commission (the "Commission"). The following documents, which are on file with the
  Commission, are incorporated in this registration statement by reference:
  (a) The registrant's latest annual report filed pursuant to Section 13(a) or 15(d) of the
  Exchange Act or the latest prospectus filed pursuant to Rule 424(b) under the Securities Act that
  contains audited financial statements for the registrant's latest fiscal year for which such
  statements have been filed.
  (b) All other reports filed pursuant to Section 13(a) or 15(d) of the Exchange Act since the
  end of the fiscal year covered by the document referred to in (a) above.
  (c) The description of the securities contained in the registrant's registration statement on
  Form 8-A filed under the Exchange Act, including any amendment or report filed for the purpose of
  updating such description.
  All documents subsequently filed by the registrant pursuant to Sections 13(a), 13(c), 14 and
  15(d) of the Exchange Act, prior to the filing of a post-effective amendment which indicates that
  all securities offered hereby have been sold or which deregisters all securities then remaining
  unsold, shall be deemed to be incorporated by reference in this registration statement and to be
  part hereof from the date of the filing of such documents. Any statement contained in a document
  incorporated or deemed to be incorporated by reference herein shall be deemed to be modified or
  superseded for the purposes of this registration statement to the extent that a statement contained
  herein or in any other subsequently filed document which also is or is deemed to be incorporated by
  reference herein modifies or supersedes such statement. Any statement so modified or superseded
  shall not be deemed, except as so modified or superseded, to constitute a part of this registration
  statement.
  Item 4. Description of Securities.
  Not applicable.
  - 1 -
  Table of Contents
  Item 5. Interests of Named Experts and Counsel.
  Wilmer Cutler Pickering Hale and Dorr LLP has opined as to the legality of the securities
  being offered by this registration statement.
  Item 6. Indemnification of Directors and Officers.
  Section 102 of the Delaware General Corporation Law allows a corporation to eliminate the
  personal liability of directors of a corporation to the corporation or its stockholders for
  monetary damages for a breach of fiduciary duty as a director, except where the director breached
  his duty of loyalty, failed to act in good faith, engaged in intentional misconduct or knowingly
  violated a law, authorized the payment of a dividend or approved a stock repurchase in violation of
  Delaware corporate law or obtained an improper personal benefit. The registrant has included such a
  provision in its Restated Certificate of Incorporation.
  Section 145 of the General Corporation Law of Delaware provides that a corporation has the
  power to indemnify a director, officer, employee or agent of the corporation and certain other
  persons serving at the request of the corporation in related capacities against amounts paid and
  expenses incurred in connection with an action or proceeding to which he is or is threatened to be
  made a party by reason of such position, if such person shall have acted in good faith and in a
  manner he reasonably believed to be in or not opposed to the best interests of the corporation,
  and, in any criminal proceeding, if such person had no reasonable cause to believe his conduct was
  unlawful; provided that, in the case of actions brought by or in the right of the corporation, no
  indemnification shall be made with respect to any matter as to which such person shall have been
  adjudged to be liable to the corporation unless and only to the extent that the adjudicating court
  determines that such indemnification is proper under the circumstances.
  The registrant's Restated Certificate of Incorporation includes a provision that eliminates
  the personal liability of its directors for monetary damages for breach of fiduciary duty as a
  director, except for liability:
  •
  for any breach of the director's duty of loyalty to the registrant or its
  stockholders;
  •
  for acts or omissions not in good faith or that involve intentional misconduct or a
  knowing violation of law;
  •
  under Section 174 of the Delaware General Corporation Law regarding unlawful
  dividends and stock purchases; or
  •
  for any transaction from which the director derived an improper personal benefit.
  These provisions are permitted under Delaware law. The registrant's Amended and Restated Bylaws
  provide that:
  •
  it must indemnify its directors and officers to the fullest extent permitted by
  Delaware law;
  •
  it may indemnify its other employees and agents to the same extent that it
  indemnified its officers and directors, unless otherwise determined by its Board of
  Directors; and
  •
  it must advance expenses, as incurred, to its directors and executive officers in
  connection with a legal proceeding to the fullest extent permitted by Delaware law.
  The indemnification provisions contained in the registrant's Restated Certificate of
  Incorporation and Amended and Restated Bylaws are not exclusive of any other rights to which a
  person may be entitled by law, agreement, vote of stockholders or disinterested directors or
  otherwise.
  - 2 -
  Table of Contents
  In addition to the indemnification provided for in the Registrant's restated certificate of
  incorporation and restated bylaws, the registrant has entered into indemnification agreements with
  each of its directors and executive officers. Each indemnification agreement provides that it will
  indemnify the director or executive officer to the fullest extent permitted by law for claims
  arising in his or her capacity as a director, officer, employee or agent of the Registrant,
  provided that he or she acted in good faith and in a manner that he or she reasonably believed to
  be in, or not opposed to, the Registrant's best interests and, with respect to any criminal
  proceeding, had no reasonable cause to believe that his or her conduct was unlawful. If the claim
  is brought by or on behalf of the Registrant, the Registrant will not be obligated to indemnify the
  director or executive officer if he or she is found liable to the Registrant, unless the court
  determines that, despite the adjudication of liability, in view of all the circumstances of the
  case the director or executive officer is fairly and reasonably entitled to be indemnified. In the
  event that the Registrant does not assume the defense of a claim against a director or executive
  officer, the Registrant is required to advance his or her expenses in connection with his or her
  defense, provided that he or she undertakes to repay all amounts advanced if it is ultimately
  determined that he or she is not entitled to be indemnified by the Registrant.
  The registrant also maintains insurance on behalf of its directors and executive officers
  insuring them against any liability asserted against them in their capacities as directors or
  officers or arising out of such status.
  Item 7. Exemption from Registration Claimed.
  Not applicable.
  Item 8. Exhibits.
  The Exhibit Index immediately preceding the exhibits is incorporated herein by reference.
  Item 9. Undertakings.
  1.
  Item
  512(a)
  of Regulation S-K
  . The undersigned registrant hereby undertakes:
  (1) To file, during any period in which offers or sales are being made, a
  post-effective amendment to this registration statement:
  (i) To include any prospectus required by Section 10(a)(3) of the Securities Act;
  (ii) To reflect in the prospectus any facts or events arising after the effective date
  of the registration statement (or the most recent post-effective amendment thereof) which,
  individually or in the aggregate, represent a fundamental change in the information set
  forth in the registration statement; and
  (iii) To include any material information with respect to the plan of distribution not
  previously disclosed in the registration statement or any material change to such
  information in the registration statement;
  provided, however,
  that paragraphs (i) and (ii) do not apply if the information required to
  be included in a post-effective amendment by those paragraphs is contained in periodic
  reports filed with or furnished to the Commission by the registrant pursuant to Section 13
  or Section 15(d) of the Exchange Act that are incorporated by reference in the registration
  statement.
  - 3 -
  Table of Contents
  (2) That, for the purpose of determining any liability under the Securities Act, each
  such post-effective amendment shall be deemed to be a new registration statement relating to
  the securities offered therein, and the offering of such securities at that time shall be
  deemed to be the initial
  bona fide
  offering thereof.
  (3) To remove from registration by means of a post-effective amendment any of the
  securities being registered which remain unsold at the termination of the offering.
  2.
  Item
  512(b)
  of Regulation S-K
  . The undersigned registrant hereby undertakes that,
  for purposes of determining any liability under the Securities Act, each filing of the registrant's
  annual report pursuant to Section 13(a) or Section 15(d) of the Exchange Act that is incorporated
  by reference in the registration statement shall be deemed to be a new registration statement
  relating to the securities offered therein, and the offering of such securities at that time shall
  be deemed to be the initial
  bona fide
  offering thereof.
  3.
  Item
  512(h)
  of Regulation S-K
  . Insofar as indemnification for liabilities arising
  under the Securities Act may be permitted to directors, officers and controlling persons of the
  registrant pursuant to the foregoing provisions, or otherwise, the registrant has been advised that
  in the opinion of the Securities and Exchange Commission such indemnification is against public
  policy as expressed in the Securities Act and is, therefore, unenforceable. In the event that a
  claim for indemnification against such liabilities (other than the payment by the registrant of
  expenses incurred or paid by a director, officer or controlling person of the registrant in the
  successful defense of any action, suit or proceeding) is asserted by such director, officer or
  controlling person in connection with the securities being registered, the registrant will, unless
  in the opinion of its counsel the matter has been settled by controlling precedent, submit to a
  court of appropriate jurisdiction the question whether such indemnification by it is against public
  policy as expressed in the Securities Act and will be governed by the final adjudication of such
  issue.
  - 4 -
  Table of Contents
  SIGNATURES
  Pursuant to the requirements of the Securities Act of 1933, the registrant certifies that it
  has reasonable grounds to believe that it meets all of the requirements for filing on Form S-8 and
  has duly caused this registration statement to be signed on its behalf by the undersigned,
  thereunto duly authorized, in Lawrence, Massachusetts on this
  9th day of December, 2005.
  NXSTAGE MEDICAL, INC.
  By:
  /s/
  Jeffrey H. Burbank
  Name:
  Jeffrey H. Burbank
  Title:
  President and Chief Executive Officer
  POWER OF ATTORNEY AND SIGNATURES
  We, the undersigned officers and directors of NxStage Medical, Inc., hereby severally
  constitute and appoint Jeffrey H. Burbank, David N. Gill and Winifred L. Swan, and each of them
  singly, our true and lawful attorneys with full power to them, and each of them singly, to sign for
  us and in our names in the capacities indicated below, the registration statement on Form S-8 filed
  herewith and any and all subsequent amendments to said registration statement, and generally to do
  all such things in our names and on our behalf in our capacities as officers and directors to
  enable NxStage Medical, Inc. to comply with the provisions of the Securities Act of 1933, as
  amended, and all requirements of the Securities and Exchange Commission, hereby ratifying and
  confirming our signatures as they may be signed by our said attorneys, or any of them, to said
  registration statement and any and all amendments thereto.
  Pursuant to the requirements of the Securities Act of 1933, this registration statement has
  been signed by the following persons in the capacities and on the dates indicated.
  Signature
  Title
  Date
  /s/ Jeffrey H. Burbank
  Chief Executive Officer
  December 9, 2005
  Jeffrey H. Burbank
  (Principal executive officer)
  /s/
  David N. Gill
  Chief Financial Officer
  December 9, 2005
  David N. Gill
  (Principal financial and
  accounting officer)
  /s/ Philippe O. Chambon, M.D., Ph.D.
  Director
  December 9, 2005
  Philippe O. Chambon, M.D., Ph.D.
  /s/ Jean-Francois Formela
  Director
  December 9, 2005
  Jean-Francois Formela
  /s/ Daniel A. Giannini
  Director
  December 9, 2005
  Daniel A. Giannini
  - 5 -
  Table of Contents
  /s/ Reid S. Perper
  Director
  December 9, 2005
  Reid S. Perper
  /s/ Peter P. Phildius
  Director
  December 9, 2005
  Peter P. Phildius
  /s/ Craig W. Moore
  Director
  December 9, 2005
  Craig W. Moore
  /s/ David S. Utterberg
  Director
  December 9, 2005
  David S. Utterberg
  - 6 -
  Table of Contents
  INDEX TO EXHIBITS
  Number
  Description
  4.1(1)
  Restated Certificate of Incorporation of the Registrant
  4.2(1)
  Restated By-Laws of the Registrant
  5
  Opinion of Wilmer Cutler Pickering Hale and Dorr LLP, counsel to
  the Registrant
  23.1
  Consent of Wilmer Cutler Pickering Hale and Dorr LLP
  (included in Exhibit 5)
  23.2
  Consent of Ernst & Young LLP
  24
  Power of attorney (included on the signature pages of this
  registration statement)
  (1)
  Previously filed with the Securities and Exchange Commission as an Exhibit to the
  Registrant's Registration Statement on Form S-1, as amended (File No. 333-126711), and
  incorporated herein by reference.