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

    <schemaVersion>X0202</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2004-05-05</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>2004-05-05</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>P</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>2000</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>22.84</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>7000</value>
                    <footnoteId id="F1"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                    <footnoteId id="F2"/>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <footnotes>
        <footnote id="F1">As of May 5, 2004, Reporting Person also owns options to purchase 15,000 shares of Issuer's Common Stock.</footnote>
        <footnote id="F2">Reporting Person, as of May 5, 2004, owns 2,000 of the 7,000 Total Beneficially Owned, Indirectly through Trust for Son.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>Thomas C. Theobald, By: T. Richard Riney, Attorney-In-Fact</signatureName>
        <signatureDate>2004-05-07</signatureDate>
    </ownerSignature>
</ownershipDocument>
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X0202
4
2004-05-05
0000740260
VENTAS INC
VTR
0001042563
THEOBALD THOMAS C
227 WEST MONROE, STE. 3500
CHICAGO
IL
60606
1
0
0
0
Common Stock
2004-05-05
4
P
0
2000
22.84
A
7000
D
As of May 5, 2004, Reporting Person also owns options to purchase 15,000 shares of Issuer's Common Stock.
Reporting Person, as of May 5, 2004, owns 2,000 of the 7,000 Total Beneficially Owned, Indirectly through Trust for Son.
Thomas C. Theobald, By: T. Richard Riney, Attorney-In-Fact
2004-05-07