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

    <schemaVersion>X0303</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2010-02-26</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>2010-02-26</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>1793</value>
                    <footnoteId id="F1"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>5441.544</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2010-02-26</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>F</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>176</value>
                    <footnoteId id="F2"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>44.19</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>5265.544</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2010-02-27</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>F</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>388</value>
                    <footnoteId id="F3"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>44.19</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>5089.841</value>
                    <footnoteId id="F4"/>
                    <footnoteId id="F5"/>
                </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>44.19</value>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2010-02-26</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>3592</value>
                    <footnoteId id="F6"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <value>2010-02-26</value>
                <footnoteId id="F7"/>
            </exerciseDate>
            <expirationDate>
                <value>2020-02-26</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>3592</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>6768</value>
                    <footnoteId id="F8"/>
                </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;). These shares vest 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 26, 2010 under the Plan.</footnote>
        <footnote id="F3">Represents shares withheld to pay the taxes on the vesting of restricted stock granted on February 27, 2009 under the Plan.</footnote>
        <footnote id="F4">Includes 50.371 shares acquired between March 31, 2009 and December 30, 2009 under the Ventas, Inc. Distribution Reinvestment and Stock Purchase Plan.</footnote>
        <footnote id="F5">Includes 161.926 shares acquired between March 3, 2009 and March 1, 2010 under the Ventas Employee and Director Stock Purchase Plan.</footnote>
        <footnote id="F6">Stock options granted by Issuer pursuant to the Plan.</footnote>
        <footnote id="F7">These options vest in three equal annual installments beginning on the date of grant.</footnote>
        <footnote id="F8">Represents total number of unexercised stock options held by the Reporting Person as of February 27, 2010.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>Julie M. Dreixler, By: T. Richard Riney, Attorney-In-Fact</signatureName>
        <signatureDate>2010-03-02</signatureDate>
    </ownerSignature>
</ownershipDocument>
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X0303
4
2010-02-26
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
2010-02-26
4
A
0
1793
0
A
5441.544
D
Common Stock
2010-02-26
4
F
0
176
44.19
D
5265.544
D
Common Stock
2010-02-27
4
F
0
388
44.19
D
5089.841
D
Stock Option (Right to Buy)
44.19
2010-02-26
4
A
0
3592
0
A
2010-02-26
2020-02-26
Common Stock
3592
6768
D
Restricted stock granted by Issuer pursuant to the Ventas, Inc. 2006 Incentive Plan (the "Plan"). These shares vest 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 26, 2010 under the Plan.
Represents shares withheld to pay the taxes on the vesting of restricted stock granted on February 27, 2009 under the Plan.
Includes 50.371 shares acquired between March 31, 2009 and December 30, 2009 under the Ventas, Inc. Distribution Reinvestment and Stock Purchase Plan.
Includes 161.926 shares acquired between March 3, 2009 and March 1, 2010 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, 2010.
Julie M. Dreixler, By: T. Richard Riney, Attorney-In-Fact
2010-03-02