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

    <schemaVersion>X0202</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2007-06-30</periodOfReport>

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

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001388433</rptOwnerCik>
            <rptOwnerName>Doman Timothy 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>Sr. V.P., Asset Management</officerTitle>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2007-06-30</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>F</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>72</value>
                    <footnoteId id="F1"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>36.25</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>4825.246</value>
                    <footnoteId id="F2"/>
                    <footnoteId id="F3"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>449</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>By Trust</value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
    </nonDerivativeTable>

    <footnotes>
        <footnote id="F1">Represents share withholding to pay tax withholding on the vesting of restricted stock previously granted to Reporting Person on June 30, 2006 under the Ventas, Inc. 2000 Incentive Compensation Plan.</footnote>
        <footnote id="F2">Includes 62.301 shares acquired under the Ventas Employee and Director Stock Purchase Plan between February 26, 2007 and July 2, 2007.</footnote>
        <footnote id="F3">As of June 30, 2007, Reporting Person also owns options to purchase 15,219 shares of Issuer's common stock.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>Timothy A. Doman, By: T. Richard Riney, Attorney-In-Fact</signatureName>
        <signatureDate>2007-07-03</signatureDate>
    </ownerSignature>
</ownershipDocument>
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X0202
4
2007-06-30
0000740260
VENTAS INC
VTR
0001388433
Doman Timothy A
10350 ORMSBY PARK PLACE, SUITE 300
LOUISVILLE
KY
40223
0
1
0
0
Sr. V.P., Asset Management
Common Stock
2007-06-30
4
F
0
72
36.25
D
4825.246
D
Common Stock
449
I
By Trust
Represents share withholding to pay tax withholding on the vesting of restricted stock previously granted to Reporting Person on June 30, 2006 under the Ventas, Inc. 2000 Incentive Compensation Plan.
Includes 62.301 shares acquired under the Ventas Employee and Director Stock Purchase Plan between February 26, 2007 and July 2, 2007.
As of June 30, 2007, Reporting Person also owns options to purchase 15,219 shares of Issuer's common stock.
Timothy A. Doman, By: T. Richard Riney, Attorney-In-Fact
2007-07-03