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

    <schemaVersion>X0202</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2006-01-27</periodOfReport>

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

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001198222</rptOwnerCik>
            <rptOwnerName>ROSENBERG SHELI  Z</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>TWO NORTH RIVERSIDE PLAZA, SUITE 600</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>CHICAGO</rptOwnerCity>
            <rptOwnerState>IL</rptOwnerState>
            <rptOwnerZipCode>60606</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>2006-01-27</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>40.545</value>
                    <footnoteId id="F1"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>30.83</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>41146.373</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 Non-Employee Director Deferred Stock Compensation Plan (&quot;Plan&quot;) in lieu of Director committee meeting 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 416.954 shares acquired on January 13, 2006 under the Ventas, Inc. Distribution Reinvestment and Stock Purchase Plan.</footnote>
        <footnote id="F3">Includes 24.379 Units acquired on January 13, 2006 under the Ventas Nonemployee Director Deferred Stock Compensation Plan as a result of dividend equivalents credited with respect to dividend paid on January 13, 2006.</footnote>
        <footnote id="F4">Includes 120.054 shares acquired on January 4, 2006 under the Ventas Employee and Director Stock Purchase Plan.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>Sheli Z. Rosenberg, By: T. Richard Riney, Attorney-In-Fact</signatureName>
        <signatureDate>2006-01-31</signatureDate>
    </ownerSignature>
</ownershipDocument>
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X0202
4
2006-01-27
0000740260
VENTAS INC
VTR
0001198222
ROSENBERG SHELI  Z
TWO NORTH RIVERSIDE PLAZA, SUITE 600
CHICAGO
IL
60606
1
0
0
0
Common Stock
2006-01-27
4
A
0
40.545
30.83
A
41146.373
D
Common Stock in the form of Units granted under the Non-Employee Director Deferred Stock Compensation Plan ("Plan") in lieu of Director committee meeting 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 416.954 shares acquired on January 13, 2006 under the Ventas, Inc. Distribution Reinvestment and Stock Purchase Plan.
Includes 24.379 Units acquired on January 13, 2006 under the Ventas Nonemployee Director Deferred Stock Compensation Plan as a result of dividend equivalents credited with respect to dividend paid on January 13, 2006.
Includes 120.054 shares acquired on January 4, 2006 under the Ventas Employee and Director Stock Purchase Plan.
Sheli Z. Rosenberg, By: T. Richard Riney, Attorney-In-Fact
2006-01-31