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

    <schemaVersion>X0304</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2011-12-31</periodOfReport>

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

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001070021</rptOwnerCik>
            <rptOwnerName>PASQUALE DOUGLAS 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>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2011-12-31</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>F</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>4054</value>
                    <footnoteId id="F1"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>55.13</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>174755</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2012-01-01</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>1028</value>
                    <footnoteId id="F2"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>175783</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2012-01-03</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>S</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
                <footnoteId id="F3"/>
                <footnoteId id="F4"/>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>20000</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>56.1346</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>155783</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>4326</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>By IRA</value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
    </nonDerivativeTable>

    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
                <value>Stock Option (Right to Buy)</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>55.13</value>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2012-01-01</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>5000</value>
                    <footnoteId id="F5"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <value>2012-01-01</value>
                <footnoteId id="F6"/>
            </exerciseDate>
            <expirationDate>
                <value>2022-01-01</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>5000</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>90660</value>
                    <footnoteId id="F7"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">Represents shares withheld to pay the taxes on the vesting and settlement of restricted stock units granted by Nationwide Health Properties, Inc. (&quot;NHP&quot;) on February 15, 2011 and assumed by the Issuer pursuant to the Agreement and Plan of Merger, dated February 27, 2011, by and among Ventas, Inc., Needles Acquisition LLC and NHP.</footnote>
        <footnote id="F2">Restricted stock granted by Issuer pursuant to the Ventas, Inc. 2006 Stock Plan for Directors (the &quot;Stock Plan&quot;).  This restricted stock vests in two equal annual installments beginning on the first anniversary of the date of grant.</footnote>
        <footnote id="F3">On January 3, 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 on Table 1. 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 $56.00 to $56.32, inclusive. Reporting Person undertakes to provide the Issuer, any security holder of the 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">These shares are being sold pursuant to a written non-discretionary Rule 10b5-1(c) sales plan dated November 23, 2011.</footnote>
        <footnote id="F5">Stock options granted by Issuer pursuant to the Stock Plan.</footnote>
        <footnote id="F6">These options vest in two equal annual installments beginning on the date of grant.</footnote>
        <footnote id="F7">Represents total number of unexercised stock options held by the Reporting Person as of January 1, 2012.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>Douglas M. Pasquale, By: T. Richard Riney, Attorney-In-Fact</signatureName>
        <signatureDate>2012-01-04</signatureDate>
    </ownerSignature>
</ownershipDocument>
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X0304
4
2011-12-31
0000740260
VENTAS INC
VTR
0001070021
PASQUALE DOUGLAS M
111 SOUTH WACKER DRIVE, SUITE 4800
CHICAGO,
IL
60606
1
0
0
0
Common Stock
2011-12-31
4
F
0
4054
55.13
D
174755
D
Common Stock
2012-01-01
4
A
0
1028
0
A
175783
D
Common Stock
2012-01-03
4
S
0
20000
56.1346
D
155783
D
Common Stock
4326
I
By IRA
Stock Option (Right to Buy)
55.13
2012-01-01
4
A
0
5000
0
A
2012-01-01
2022-01-01
Common Stock
5000
90660
D
Represents shares withheld to pay the taxes on the vesting and settlement of restricted stock units granted by Nationwide Health Properties, Inc. ("NHP") on February 15, 2011 and assumed by the Issuer pursuant to the Agreement and Plan of Merger, dated February 27, 2011, by and among Ventas, Inc., Needles Acquisition LLC and NHP.
Restricted stock granted by Issuer pursuant to the Ventas, Inc. 2006 Stock Plan for Directors (the "Stock Plan").  This restricted stock vests in two equal annual installments beginning on the first anniversary of the date of grant.
On January 3, 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 on Table 1. 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 $56.00 to $56.32, inclusive. Reporting Person undertakes to provide the Issuer, any security holder of the 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).
These shares are being sold pursuant to a written non-discretionary Rule 10b5-1(c) sales plan dated November 23, 2011.
Stock options granted by Issuer pursuant to the Stock Plan.
These options vest in two equal annual installments beginning on the date of grant.
Represents total number of unexercised stock options held by the Reporting Person as of January 1, 2012.
Douglas M. Pasquale, By: T. Richard Riney, Attorney-In-Fact
2012-01-04