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

    <schemaVersion>X0202</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2007-01-17</periodOfReport>

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

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001215187</rptOwnerCik>
            <rptOwnerName>LEWIS RAYMOND J</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>Ex.VP.Chief Investment Officer</officerTitle>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2007-01-17</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>7281</value>
                    <footnoteId id="F1"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>38334</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2007-01-17</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>F</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>1078</value>
                    <footnoteId id="F2"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>43.26</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>37256</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2007-01-18</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>F</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>951</value>
                    <footnoteId id="F3"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>43.28</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>36305</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
                <value>Stock Option (Right to Buy)</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>43.26</value>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2007-01-17</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>31658</value>
                    <footnoteId id="F4"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <value>2007-01-17</value>
                <footnoteId id="F5"/>
            </exerciseDate>
            <expirationDate>
                <value>2017-01-17</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>31658</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>187956</value>
                    <footnoteId id="F6"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">These shares represent restricted shares granted under the Ventas, Inc. 2006 Incentive Plan (the &quot;Plan&quot;) on January 17, 2007.  These shares vest in cumulative 1/3 annual installments beginning on January 17, 2007.</footnote>
        <footnote id="F2">Represents share withholding  to pay tax withholding on the first vesting of restricted stock granted on January 17, 2007 under the Plan.</footnote>
        <footnote id="F3">Represents share withholding to pay tax withholding on the vesting of restricted stock previously granted to Reporting Person on January 18, 2005 under the Ventas, Inc. 2000 Incentive Compensation Plan.</footnote>
        <footnote id="F4">These stock options represent stock options granted under the Plan on January 17, 2007.</footnote>
        <footnote id="F5">These options vest in cumulative 1/3 annual installments beginning on January 17, 2007.</footnote>
        <footnote id="F6">Represents total number of unexercised stock options held by the Reporting Person as of January 18, 2007.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>Raymond J. Lewis, By: T. Richard Riney, Attorney-In-Fact</signatureName>
        <signatureDate>2007-01-19</signatureDate>
    </ownerSignature>
</ownershipDocument>
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X0202
4
2007-01-17
0000740260
VENTAS INC
VTR
0001215187
LEWIS RAYMOND J
10350 ORMSBY PARK PLACE, SUITE 300
LOUISVILLE
KY
40223
0
1
0
0
Ex.VP.Chief Investment Officer
Common Stock
2007-01-17
4
A
0
7281
0
A
38334
D
Common Stock
2007-01-17
4
F
0
1078
43.26
D
37256
D
Common Stock
2007-01-18
4
F
0
951
43.28
D
36305
D
Stock Option (Right to Buy)
43.26
2007-01-17
4
A
0
31658
0
A
2007-01-17
2017-01-17
Common Stock
31658
187956
D
These shares represent restricted shares granted under the Ventas, Inc. 2006 Incentive Plan (the "Plan") on January 17, 2007.  These shares vest in cumulative 1/3 annual installments beginning on January 17, 2007.
Represents share withholding  to pay tax withholding on the first vesting of restricted stock granted on January 17, 2007 under the Plan.
Represents share withholding to pay tax withholding on the vesting of restricted stock previously granted to Reporting Person on January 18, 2005 under the Ventas, Inc. 2000 Incentive Compensation Plan.
These stock options represent stock options granted under the Plan on January 17, 2007.
These options vest in cumulative 1/3 annual installments beginning on January 17, 2007.
Represents total number of unexercised stock options held by the Reporting Person as of January 18, 2007.
Raymond J. Lewis, By: T. Richard Riney, Attorney-In-Fact
2007-01-19