<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0304</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2011-11-02</periodOfReport>

    <issuer>
        <issuerCik>0000740260</issuerCik>
        <issuerName>VENTAS INC</issuerName>
        <issuerTradingSymbol>VTR</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001203367</rptOwnerCik>
            <rptOwnerName>LUSTIG MATTHEW J</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>30 ROCKEFELLER PLAZA</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>NEW YORK,</rptOwnerCity>
            <rptOwnerState>NY</rptOwnerState>
            <rptOwnerZipCode>10020</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2011-11-02</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>J</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>83441</value>
                    <footnoteId id="F1"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>24770619</value>
                    <footnoteId id="F2"/>
                    <footnoteId id="F3"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>See Footnote</value>
                    <footnoteId id="F2"/>
                    <footnoteId id="F3"/>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>3387.625</value>
                    <footnoteId id="F4"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
    </nonDerivativeTable>

    <footnotes>
        <footnote id="F1">Represents shares of common stock, par value $0.25 (&quot;Common Stock&quot;), of Ventas, Inc., a Delaware corporation (the &quot;Issuer&quot;), owned by the Funds (as defined below) and cancelled by the Issuer in connection with the settlement of the post-closing merger consideration adjustment set forth in the merger agreement relating to the Issuer's acquisition (the &quot;Transaction&quot;) of substantially all of the real estate assets of Atria Senior Living Group, Inc., a Delaware corporation, One Lantern Senior Living Inc., a Delaware corporation, and LSHP Coinvestment I Inc., a Delaware corporation, and the allocation between the Issuer and the Funds of certain taxes and expenses related to the Transaction.</footnote>
        <footnote id="F2">Prometheus Senior Quarters LLC, a Delaware limited liability company (&quot;Prometheus&quot;), Lazard Senior Housing Partners LP, a Delaware limited partnership (&quot;LSHP&quot;), and LSHP Coinvestment Partnership I LP, a Delaware limited partnership (&quot;LSHP Coinvest&quot;, together with Prometheus and LSHP, the &quot;Funds&quot;), collectively, may be deemed to beneficially own 24,770,619 shares of Common Stock. The Managing Members of Prometheus are LFSRI II-CADIM Alternative Partnership L.P., LF Strategic Realty Investors II L.P. and LFSRI II Alternative Partnership L.P., each a Delaware limited partnership, and Lazard Freres Real Estate Investors L.L.C., a New York limited liability company (&quot;LFREI&quot;), is the general partner of each such limited partnership. Lazard Senior Housing Partners GP LLC, a Delaware limited liability company (&quot;LSHP GP&quot;), is the general partner of LSHP. LSHP Coinvestment I GP LLC, a Delaware limited liability company (&quot;LSHP Coinvest GP&quot;), is the general partner of LSHP Coinvest.</footnote>
        <footnote id="F3">[Continued from previous] Lazard Alternative Investments LLC, a Delaware limited liability company (&quot;LAI&quot;), is the managing member of each of LFREI, LSHP GP and LSHP Coinvest GP. In his capacity as Managing Director of LAI, Managing Principal of LFREI, and Managing Principal and Chief Executive Officer of each of LSHP GP and LSHP Coinvest GP, Mr. Lustig may be deemed to be the beneficial owner of the securitiies reported herein. Mr. Lustig expressly disclaims beneficial ownership of the securities reported herein, except to the extent of his pecuniary interest therein, if any.</footnote>
        <footnote id="F4">Includes 2,656 shares of restricted stock granted by the Issuer pursuant to the Ventas, Inc. 2006 Stock Plan for Directors and 731.625 shares of Common Stock in the form of Units granted under the Ventas Nonemployee Director Deferred Stock Compensation Plan (the &quot;Plan&quot;).  Such Units are payable solely in Common Stock and subject to the terms and conditions of the Director's deferral election and the Plan.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>Matthew J. Lustig, By: T. Richard Riney, Attorney-In-Fact</signatureName>
        <signatureDate>2011-11-02</signatureDate>
    </ownerSignature>
</ownershipDocument>
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X0304
4
2011-11-02
0000740260
VENTAS INC
VTR
0001203367
LUSTIG MATTHEW J
30 ROCKEFELLER PLAZA
NEW YORK,
NY
10020
1
0
0
0
Common Stock
2011-11-02
4
J
0
83441
0
D
24770619
I
See Footnote
Common Stock
3387.625
D
Represents shares of common stock, par value $0.25 ("Common Stock"), of Ventas, Inc., a Delaware corporation (the "Issuer"), owned by the Funds (as defined below) and cancelled by the Issuer in connection with the settlement of the post-closing merger consideration adjustment set forth in the merger agreement relating to the Issuer's acquisition (the "Transaction") of substantially all of the real estate assets of Atria Senior Living Group, Inc., a Delaware corporation, One Lantern Senior Living Inc., a Delaware corporation, and LSHP Coinvestment I Inc., a Delaware corporation, and the allocation between the Issuer and the Funds of certain taxes and expenses related to the Transaction.
Prometheus Senior Quarters LLC, a Delaware limited liability company ("Prometheus"), Lazard Senior Housing Partners LP, a Delaware limited partnership ("LSHP"), and LSHP Coinvestment Partnership I LP, a Delaware limited partnership ("LSHP Coinvest", together with Prometheus and LSHP, the "Funds"), collectively, may be deemed to beneficially own 24,770,619 shares of Common Stock. The Managing Members of Prometheus are LFSRI II-CADIM Alternative Partnership L.P., LF Strategic Realty Investors II L.P. and LFSRI II Alternative Partnership L.P., each a Delaware limited partnership, and Lazard Freres Real Estate Investors L.L.C., a New York limited liability company ("LFREI"), is the general partner of each such limited partnership. Lazard Senior Housing Partners GP LLC, a Delaware limited liability company ("LSHP GP"), is the general partner of LSHP. LSHP Coinvestment I GP LLC, a Delaware limited liability company ("LSHP Coinvest GP"), is the general partner of LSHP Coinvest.
[Continued from previous] Lazard Alternative Investments LLC, a Delaware limited liability company ("LAI"), is the managing member of each of LFREI, LSHP GP and LSHP Coinvest GP. In his capacity as Managing Director of LAI, Managing Principal of LFREI, and Managing Principal and Chief Executive Officer of each of LSHP GP and LSHP Coinvest GP, Mr. Lustig may be deemed to be the beneficial owner of the securitiies reported herein. Mr. Lustig expressly disclaims beneficial ownership of the securities reported herein, except to the extent of his pecuniary interest therein, if any.
Includes 2,656 shares of restricted stock granted by the Issuer pursuant to the Ventas, Inc. 2006 Stock Plan for Directors and 731.625 shares of Common Stock in the form of Units granted under the Ventas Nonemployee Director Deferred Stock Compensation Plan (the "Plan").  Such Units are payable solely in Common Stock and subject to the terms and conditions of the Director's deferral election and the Plan.
Matthew J. Lustig, By: T. Richard Riney, Attorney-In-Fact
2011-11-02