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

    <schemaVersion>X0303</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2011-01-01</periodOfReport>

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

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001188136</rptOwnerCik>
            <rptOwnerName>SHELTON JAMES D</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>2800 NORTH DALLAS PARKWAY, SUITE 200</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>PLANO</rptOwnerCity>
            <rptOwnerState>TX</rptOwnerState>
            <rptOwnerZipCode>75093</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>2011-01-01</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>119.093</value>
                    <footnoteId id="F1"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>52.48</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>6023.222</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2011-01-01</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>1025</value>
                    <footnoteId id="F2"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>7048.222</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>52.48</value>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2011-01-01</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>5000</value>
                    <footnoteId id="F3"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <value>2011-01-01</value>
                <footnoteId id="F4"/>
            </exerciseDate>
            <expirationDate>
                <value>2021-01-01</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>5000</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>15000</value>
                    <footnoteId id="F5"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">Common Stock in the form of Units granted under the Ventas Nonemployee Director Deferred Stock Compensation Plan (the &quot;Plan&quot;) in lieu of Director fees pursuant to the Director's deferral election.  Such Units are payable solely in Common Stock and subject to the terms and conditions of the Director's deferral election and the Plan.</footnote>
        <footnote id="F2">Restricted stock granted by Issuer pursuant to the Ventas, Inc. 2006 Stock Plan for Directors (the &quot;Stock Plan&quot;). These shares vest in two equal annual installments beginning on the first anniversary of the date of grant.</footnote>
        <footnote id="F3">Stock options granted by Issuer pursuant to the Stock Plan.</footnote>
        <footnote id="F4">These options vest in two equal annual installments beginning on the date of grant.</footnote>
        <footnote id="F5">Represents total number of unexercised stock options owned by the Reporting Person as of January 1, 2011.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>James D. Shelton, By: T. Richard Riney, Attorney-In-Fact</signatureName>
        <signatureDate>2011-01-04</signatureDate>
    </ownerSignature>
</ownershipDocument>
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X0303
4
2011-01-01
0000740260
VENTAS INC
VTR
0001188136
SHELTON JAMES D
2800 NORTH DALLAS PARKWAY, SUITE 200
PLANO
TX
75093
1
0
0
0
Common Stock
2011-01-01
4
A
0
119.093
52.48
A
6023.222
D
Common Stock
2011-01-01
4
A
0
1025
0
A
7048.222
D
Stock Option (Right to Buy)
52.48
2011-01-01
4
A
0
5000
0
A
2011-01-01
2021-01-01
Common Stock
5000
15000
D
Common Stock in the form of Units granted under the Ventas Nonemployee Director Deferred Stock Compensation Plan (the "Plan") in lieu of Director fees pursuant to the Director's deferral election.  Such Units are payable solely in Common Stock and subject to the terms and conditions of the Director's deferral election and the Plan.
Restricted stock granted by Issuer pursuant to the Ventas, Inc. 2006 Stock Plan for Directors (the "Stock Plan"). These shares vest in two equal annual installments beginning on the first anniversary of the date of grant.
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 owned by the Reporting Person as of January 1, 2011.
James D. Shelton, By: T. Richard Riney, Attorney-In-Fact
2011-01-04