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

    <schemaVersion>X0303</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2010-04-01</periodOfReport>

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

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001213928</rptOwnerCik>
            <rptOwnerName>GELLERT JAY M</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>21650 OXNARD ST., 22ND FLOOR</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>WOODLAND HILLS</rptOwnerCity>
            <rptOwnerState>CA</rptOwnerState>
            <rptOwnerZipCode>91367</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>2010-04-01</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>263.769</value>
                    <footnoteId id="F1"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>47.39</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>37215.849</value>
                    <footnoteId id="F2"/>
                    <footnoteId id="F3"/>
                    <footnoteId id="F4"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <footnotes>
        <footnote id="F1">Common Stock in the form of Units granted under the Ventas Nonemployee Director 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 116.004 Units acquired on March 31, 2010, under the Plan as a result of dividend equivalents credited with respect to the dividend on Issuer's common stock paid on March 31, 2010.</footnote>
        <footnote id="F3">Includes 206.44 shares acquired on March 31, 2010, under the Ventas, Inc. Distribution Reinvestment and Stock Purchase Plan.</footnote>
        <footnote id="F4">As of April 1, 2010, Reporting Person also owns options to purchase 55,000 shares of Issuer's common stock.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>Jay M. Gellert, By: T. Richard Riney, Attorney-In-Fact</signatureName>
        <signatureDate>2010-04-05</signatureDate>
    </ownerSignature>
</ownershipDocument>
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X0303
4
2010-04-01
0000740260
VENTAS INC
VTR
0001213928
GELLERT JAY M
21650 OXNARD ST., 22ND FLOOR
WOODLAND HILLS
CA
91367
1
0
0
0
Common Stock
2010-04-01
4
A
0
263.769
47.39
A
37215.849
D
Common Stock in the form of Units granted under the Ventas Nonemployee Director 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 116.004 Units acquired on March 31, 2010, under the Plan as a result of dividend equivalents credited with respect to the dividend on Issuer's common stock paid on March 31, 2010.
Includes 206.44 shares acquired on March 31, 2010, under the Ventas, Inc. Distribution Reinvestment and Stock Purchase Plan.
As of April 1, 2010, Reporting Person also owns options to purchase 55,000 shares of Issuer's common stock.
Jay M. Gellert, By: T. Richard Riney, Attorney-In-Fact
2010-04-05