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

    <schemaVersion>X0202</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2007-11-30</periodOfReport>

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

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001215189</rptOwnerCik>
            <rptOwnerName>SCHWEINHART RICHARD A</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>10350 ORMSBY PARK PLACE, SUITE 300</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>LOUISVILLE,</rptOwnerCity>
            <rptOwnerState>KY</rptOwnerState>
            <rptOwnerZipCode>40223</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>EVP, Chief Financial Officer</officerTitle>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2007-11-30</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>22935</value>
                    <footnoteId id="F1"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>69607.915</value>
                    <footnoteId id="F2"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>1605</value>
                    <footnoteId id="F3"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>By IRA</value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
    </nonDerivativeTable>

    <footnotes>
        <footnote id="F1">These shares represent restricted shares granted under the Ventas, Inc. 2006 Incentive Plan on November 30, 2007.  These shares vest in cumulative 1/3 annual installments beginning on November 30, 2010.</footnote>
        <footnote id="F2">Includes 510.199 shares acquired under Ventas Employee and Director Stock Purchase Plan between February 2, 2007 and November 2, 2007.  Amount of securities benefically owned has been adjusted to exclude 1,605 shares held indirectly by IRA.</footnote>
        <footnote id="F3">As of November 30, 2007, Reporting Person also owns options to purchase 166,001 shares of Issuer's common stock.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>Richard A. Schweinhart, By: T. Richard Riney, Attorney-In-Fact</signatureName>
        <signatureDate>2007-12-04</signatureDate>
    </ownerSignature>
</ownershipDocument>
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X0202
4
2007-11-30
0000740260
VENTAS INC
VTR
0001215189
SCHWEINHART RICHARD A
10350 ORMSBY PARK PLACE, SUITE 300
LOUISVILLE,
KY
40223
0
1
0
0
EVP, Chief Financial Officer
Common Stock
2007-11-30
4
A
0
22935
0
A
69607.915
D
Common Stock
1605
I
By IRA
These shares represent restricted shares granted under the Ventas, Inc. 2006 Incentive Plan on November 30, 2007.  These shares vest in cumulative 1/3 annual installments beginning on November 30, 2010.
Includes 510.199 shares acquired under Ventas Employee and Director Stock Purchase Plan between February 2, 2007 and November 2, 2007.  Amount of securities benefically owned has been adjusted to exclude 1,605 shares held indirectly by IRA.
As of November 30, 2007, Reporting Person also owns options to purchase 166,001 shares of Issuer's common stock.
Richard A. Schweinhart, By: T. Richard Riney, Attorney-In-Fact
2007-12-04