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

    <schemaVersion>X0306</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2012-08-01</periodOfReport>

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

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001215188</rptOwnerCik>
            <rptOwnerName>CAFARO DEBRA A</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>353 N. CLARK STREET, SUITE 3300</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>CHICAGO,</rptOwnerCity>
            <rptOwnerState>IL</rptOwnerState>
            <rptOwnerZipCode>60654</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>Chairman and CEO</officerTitle>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2012-08-01</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>M</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>95534</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>28.96</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>786886</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2012-08-01</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>S</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
                <footnoteId id="F1"/>
                <footnoteId id="F2"/>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>211400</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>67.225</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>575486</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2012-08-01</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>S</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
                <footnoteId id="F1"/>
                <footnoteId id="F3"/>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>12064</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>67.8926</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>563422</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2012-08-02</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>S</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
                <footnoteId id="F1"/>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>10800</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>67.00</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>552622</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2012-08-01</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>M</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>30000</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>28.96</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>35000</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>By Trust</value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2012-08-01</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>S</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
                <footnoteId id="F4"/>
                <footnoteId id="F5"/>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>28369</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>67.2247</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>6631</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>By Trust</value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2012-08-01</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>S</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
                <footnoteId id="F4"/>
                <footnoteId id="F6"/>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>1631</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>67.8933</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>5000</value>
                    <footnoteId id="F7"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>By Trust</value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
                <value>Stock Option (Right to Buy)</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>28.96</value>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2012-08-01</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>M</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>95534</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <value>2009-01-21</value>
                <footnoteId id="F8"/>
            </exerciseDate>
            <expirationDate>
                <value>2019-01-21</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>95534</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>668669</value>
                    <footnoteId id="F9"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </derivativeTransaction>
        <derivativeTransaction>
            <securityTitle>
                <value>Stock Option (Right to Buy)</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>28.96</value>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2012-08-01</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>M</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>30000</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <value>2009-01-21</value>
                <footnoteId id="F8"/>
            </exerciseDate>
            <expirationDate>
                <value>2019-01-21</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>30000</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>392720</value>
                    <footnoteId id="F10"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>By Trust</value>
                </natureOfOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">On August 1, 2012, the Reporting Person transmitted to the Securities and Exchange Commission (the &quot;SEC&quot;) a Form 144 covering the sale of the Issuer's common stock reported in Table I.  These shares are being sold pursuant to a written non-discretionary 10b5-1(c) sales plan dated June 29, 2012 entered into by the Reporting Person.</footnote>
        <footnote id="F2">The price reported in column 4 is a weighted average price. These shares were sold by the Reporting Person in multiple transactions at prices ranging from $66.7600 to $67.7500, inclusive. The Reporting Person  undertakes to provide Issuer, any security holder of Issuer or the staff of the SEC, upon request, full information regarding the number of shares sold at each separate price within the range set forth in this footnote (2).</footnote>
        <footnote id="F3">The price reported in column 4 is a weighted average price. These shares were sold by the Reporting Person in multiple transactions at prices ranging from $67.7600 to $68.0186, inclusive.  The Reporting Person undertakes to provide Issuer, any security holder of Issuer or the staff of the SEC, upon request, full information regarding the number of shares sold at each separate price within the range set forth in this footnote (3).</footnote>
        <footnote id="F4">On August 1, 2012, The Debra A. Cafaro Insurance Trust (the &quot;Trust&quot;) (of which Reporting Person's spouse is the trustee) transmitted to the SEC a Form 144 covering the sale of the Issuer's common stock reported in Table I.  These shares are being sold pursuant to a written non-discretionary 10b5-1(c) sales plan dated June 29, 2012 entered into by the Trust.</footnote>
        <footnote id="F5">The price reported in column 4 is a weighted average price. These shares were sold by the Trust in multiple transactions at prices ranging from $66.7600 to $67.7500, inclusive.  The Trust undertakes to provide Issuer, any security holder of Issuer or the staff of the SEC, upon request, full information regarding the number of shares sold at each separate price within the range set forth in this footnote (5).</footnote>
        <footnote id="F6">The price reported in column 4 is a weighted average price. These shares were sold by the Trust in multiple transactions at prices ranging from $67.7600 to $68.0186, inclusive.  The Trust undertakes to provide Issuer, any security holder of Issuer or the staff of the SEC, upon request, full information regarding the number of shares sold at each separate price within the range set forth in this footnote (6).</footnote>
        <footnote id="F7">Reporting Person disclaims beneficial ownership of these 5,000 shares except to the extent of the Reporting Person's pecuniary interest in the shares.</footnote>
        <footnote id="F8">These options were part of a previously reported grant of 173,301 on January 21, 2009 by the Issuer to the Reporting Person that vested in three equal annual installments beginning on January 21, 2009.</footnote>
        <footnote id="F9">Represents total number of unexercised options held directly by the Reporting Person as of August 1, 2012.</footnote>
        <footnote id="F10">Represents total number of unexercised options held indirectly by the Reporting Person as of August 1, 2012.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>Debra A. Cafaro, By: T. Richard Riney, Attorney-in-Fact</signatureName>
        <signatureDate>2012-08-03</signatureDate>
    </ownerSignature>
</ownershipDocument>
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X0306
4
2012-08-01
0000740260
VENTAS INC
VTR
0001215188
CAFARO DEBRA A
353 N. CLARK STREET, SUITE 3300
CHICAGO,
IL
60654
1
1
0
0
Chairman and CEO
Common Stock
2012-08-01
4
M
0
95534
28.96
A
786886
D
Common Stock
2012-08-01
4
S
0
211400
67.225
D
575486
D
Common Stock
2012-08-01
4
S
0
12064
67.8926
D
563422
D
Common Stock
2012-08-02
4
S
0
10800
67.00
D
552622
D
Common Stock
2012-08-01
4
M
0
30000
28.96
A
35000
I
By Trust
Common Stock
2012-08-01
4
S
0
28369
67.2247
D
6631
I
By Trust
Common Stock
2012-08-01
4
S
0
1631
67.8933
D
5000
I
By Trust
Stock Option (Right to Buy)
28.96
2012-08-01
4
M
0
95534
0
D
2009-01-21
2019-01-21
Common Stock
95534
668669
D
Stock Option (Right to Buy)
28.96
2012-08-01
4
M
0
30000
0
D
2009-01-21
2019-01-21
Common Stock
30000
392720
I
By Trust
On August 1, 2012, the Reporting Person transmitted to the Securities and Exchange Commission (the "SEC") a Form 144 covering the sale of the Issuer's common stock reported in Table I.  These shares are being sold pursuant to a written non-discretionary 10b5-1(c) sales plan dated June 29, 2012 entered into by the Reporting Person.
The price reported in column 4 is a weighted average price. These shares were sold by the Reporting Person in multiple transactions at prices ranging from $66.7600 to $67.7500, inclusive. The Reporting Person  undertakes to provide Issuer, any security holder of Issuer or the staff of the SEC, upon request, full information regarding the number of shares sold at each separate price within the range set forth in this footnote (2).
The price reported in column 4 is a weighted average price. These shares were sold by the Reporting Person in multiple transactions at prices ranging from $67.7600 to $68.0186, inclusive.  The Reporting Person undertakes to provide Issuer, any security holder of Issuer or the staff of the SEC, upon request, full information regarding the number of shares sold at each separate price within the range set forth in this footnote (3).
On August 1, 2012, The Debra A. Cafaro Insurance Trust (the "Trust") (of which Reporting Person's spouse is the trustee) transmitted to the SEC a Form 144 covering the sale of the Issuer's common stock reported in Table I.  These shares are being sold pursuant to a written non-discretionary 10b5-1(c) sales plan dated June 29, 2012 entered into by the Trust.
The price reported in column 4 is a weighted average price. These shares were sold by the Trust in multiple transactions at prices ranging from $66.7600 to $67.7500, inclusive.  The Trust undertakes to provide Issuer, any security holder of Issuer or the staff of the SEC, upon request, full information regarding the number of shares sold at each separate price within the range set forth in this footnote (5).
The price reported in column 4 is a weighted average price. These shares were sold by the Trust in multiple transactions at prices ranging from $67.7600 to $68.0186, inclusive.  The Trust undertakes to provide Issuer, any security holder of Issuer or the staff of the SEC, upon request, full information regarding the number of shares sold at each separate price within the range set forth in this footnote (6).
Reporting Person disclaims beneficial ownership of these 5,000 shares except to the extent of the Reporting Person's pecuniary interest in the shares.
These options were part of a previously reported grant of 173,301 on January 21, 2009 by the Issuer to the Reporting Person that vested in three equal annual installments beginning on January 21, 2009.
Represents total number of unexercised options held directly by the Reporting Person as of August 1, 2012.
Represents total number of unexercised options held indirectly by the Reporting Person as of August 1, 2012.
Debra A. Cafaro, By: T. Richard Riney, Attorney-in-Fact
2012-08-03