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

    <schemaVersion>X0303</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2009-02-27</periodOfReport>

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

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001422747</rptOwnerCik>
            <rptOwnerName>Dreixler Julie M.</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>111 SOUTH WACKER DRIVE, SUITE 4800</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>CHICAGO</rptOwnerCity>
            <rptOwnerState>IL</rptOwnerState>
            <rptOwnerZipCode>60606</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>SVP-Human Resources</officerTitle>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2009-02-27</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>3960</value>
                    <footnoteId id="F1"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>3960</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2009-02-27</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>F</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>389</value>
                    <footnoteId id="F2"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>21.57</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>3648.544</value>
                    <footnoteId id="F3"/>
                </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>21.57</value>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2009-02-27</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>3176</value>
                    <footnoteId id="F4"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <value>2009-02-27</value>
                <footnoteId id="F5"/>
            </exerciseDate>
            <expirationDate>
                <value>2019-02-27</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>3176</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>3176</value>
                    <footnoteId id="F6"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">Restricted stock granted by Issuer pursuant to the Ventas, Inc. 2006 Incentive Plan (the &quot;Plan&quot;).  This restricted stock vests in three equal annual installments beginning on the date of grant.</footnote>
        <footnote id="F2">Represents shares withheld to pay the taxes on the vesting of restricted stock granted on February 27, 2009 under the Plan.</footnote>
        <footnote id="F3">Includes 77.544 shares acquired between  September 3, 2008 and March 2, 2009 under the Ventas Employee and Director Stock Purchase Plan.</footnote>
        <footnote id="F4">Stock options granted by Issuer pursuant to the Plan.</footnote>
        <footnote id="F5">These options vest in three equal annual installments beginning on the date of grant.</footnote>
        <footnote id="F6">Represents total number of unexercised stock options held by the Reporting Person as of February 27, 2009.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>Julie M. Dreixler, By: T. Richard Riney, Attorney-In-Fact</signatureName>
        <signatureDate>2009-03-03</signatureDate>
    </ownerSignature>
</ownershipDocument>
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X0303
4
2009-02-27
0000740260
VENTAS INC
VTR
0001422747
Dreixler Julie M.
111 SOUTH WACKER DRIVE, SUITE 4800
CHICAGO
IL
60606
0
1
0
0
SVP-Human Resources
Common Stock
2009-02-27
4
A
0
3960
0
A
3960
D
Common Stock
2009-02-27
4
F
0
389
21.57
D
3648.544
D
Stock Option (Right to Buy)
21.57
2009-02-27
4
A
0
3176
0
A
2009-02-27
2019-02-27
Common Stock
3176
3176
D
Restricted stock granted by Issuer pursuant to the Ventas, Inc. 2006 Incentive Plan (the "Plan").  This restricted stock vests in three equal annual installments beginning on the date of grant.
Represents shares withheld to pay the taxes on the vesting of restricted stock granted on February 27, 2009 under the Plan.
Includes 77.544 shares acquired between  September 3, 2008 and March 2, 2009 under the Ventas Employee and Director Stock Purchase Plan.
Stock options granted by Issuer pursuant to the Plan.
These options vest in three equal annual installments beginning on the date of grant.
Represents total number of unexercised stock options held by the Reporting Person as of February 27, 2009.
Julie M. Dreixler, By: T. Richard Riney, Attorney-In-Fact
2009-03-03