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

    <schemaVersion>X0202</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2007-01-14</periodOfReport>

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

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001042563</rptOwnerCik>
            <rptOwnerName>THEOBALD THOMAS C</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>227 WEST MONROE, STE. 3500</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>2007-01-14</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>35.203</value>
                    <footnoteId id="F1"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>42.61</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>16328.027</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>2000</value>
                    <footnoteId id="F2"/>
                    <footnoteId id="F3"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>By Trust</value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
    </nonDerivativeTable>

    <footnotes>
        <footnote id="F1">Common Stock in the form of Units granted under the Non-Employee 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 40.235 Units acquired on January 12, 2007, under the Ventas Nonemployee Director Deferred Stock Compensation Plan as a result of dividend equivalents credited with respect to the dividend paid on Issuer's Common Stock on January 12, 2007.</footnote>
        <footnote id="F3">As of January 14, 2007, Reporting Person also owns options to purchase 30,000 shares of Issuer's common stock.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>Thomas C. Theobald, By: T. Richard Riney, Attorney-In-Fact</signatureName>
        <signatureDate>2007-01-16</signatureDate>
    </ownerSignature>
</ownershipDocument>
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X0202
4
2007-01-14
0000740260
VENTAS INC
VTR
0001042563
THEOBALD THOMAS C
227 WEST MONROE, STE. 3500
CHICAGO
IL
60606
1
0
0
0
Common Stock
2007-01-14
4
A
0
35.203
42.61
A
16328.027
D
Common Stock
2000
I
By Trust
Common Stock in the form of Units granted under the Non-Employee 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 40.235 Units acquired on January 12, 2007, under the Ventas Nonemployee Director Deferred Stock Compensation Plan as a result of dividend equivalents credited with respect to the dividend paid on Issuer's Common Stock on January 12, 2007.
As of January 14, 2007, Reporting Person also owns options to purchase 30,000 shares of Issuer's common stock.
Thomas C. Theobald, By: T. Richard Riney, Attorney-In-Fact
2007-01-16