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

    <schemaVersion>X0306</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2012-07-01</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>2012-07-01</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>297.053</value>
                    <footnoteId id="F1"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>63.12</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>5501.39</value>
                    <footnoteId id="F2"/>
                    <footnoteId id="F3"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>3700186</value>
                    <footnoteId id="F4"/>
                    <footnoteId id="F5"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>See Footnotes (4) and (5)</value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
    </nonDerivativeTable>

    <footnotes>
        <footnote id="F1">Common stock in the form of units granted under the Ventas Nonemployee Directors' Deferred Stock Compensation Plan (the &quot;Plan&quot;) in lieu of director fees pursuant to the director's deferral election.  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>
        <footnote id="F2">Includes 14.788 units acquired on June 29, 2012, under the Plan as a result of dividend equivalents credited with respect to the dividend on Issuer's common stock paid on June 29, 2012.</footnote>
        <footnote id="F3">As of July 1, 2012, Reporting Person also owns options to purchase 8,191 shares of Issuer's common stock.</footnote>
        <footnote id="F4">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;), collectively, may be deemed to beneficially own 3,700,186 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="F5">[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 securities 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>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>Matthew J. Lustig, By: T. Richard Riney, Attorney-In-Fact</signatureName>
        <signatureDate>2012-07-03</signatureDate>
    </ownerSignature>
</ownershipDocument>
[{"type": "4", "sequence": "1", "filename": "edgar.xml", "description": "PRIMARY DOCUMENT", "secsgml_size_bytes": 6308}]
X0306
4
2012-07-01
0000740260
VENTAS INC
VTR
0001203367
LUSTIG MATTHEW J
30 ROCKEFELLER PLAZA
NEW YORK,
NY
10020
1
0
0
0
Common Stock
2012-07-01
4
A
0
297.053
63.12
A
5501.39
D
Common Stock
3700186
I
See Footnotes (4) and (5)
Common stock in the form of units granted under the Ventas Nonemployee Directors' Deferred Stock Compensation Plan (the "Plan") in lieu of director fees pursuant to the director's deferral election.  Such units are payable solely in common stock and subject to the terms and conditions of the director's deferral election and the Plan.
Includes 14.788 units acquired on June 29, 2012, under the Plan as a result of dividend equivalents credited with respect to the dividend on Issuer's common stock paid on June 29, 2012.
As of July 1, 2012, Reporting Person also owns options to purchase 8,191 shares of Issuer's common stock.
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"), collectively, may be deemed to beneficially own 3,700,186 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 securities reported herein.  Mr. Lustig expressly disclaims beneficial ownership of the securities reported herein, except to the extent of his pecuniary interest therein, if any.
Matthew J. Lustig, By: T. Richard Riney, Attorney-In-Fact
2012-07-03