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

    <schemaVersion>X0304</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2011-12-23</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>2011-12-23</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>S</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
                <footnoteId id="F1"/>
                <footnoteId id="F4"/>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>20064</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>54.6093</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>218745</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2011-12-27</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>S</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
                <footnoteId id="F2"/>
                <footnoteId id="F4"/>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>38486</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>55.2561</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>180259</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2011-12-28</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>S</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
                <footnoteId id="F3"/>
                <footnoteId id="F4"/>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>200</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>55.50</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>180059</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>
                    <footnoteId id="F5"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>By IRA</value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
    </nonDerivativeTable>

    <footnotes>
        <footnote id="F1">On December 23, 2011, 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 I. 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 $54.50 to $55.00, 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 (1).</footnote>
        <footnote id="F2">On December 27, 2011, the Reporting Person transmitted to the SEC a Form 144 covering the sale of the Issuer's common stock reported on Table I. 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 $55.00 to $55.55, 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 (2).</footnote>
        <footnote id="F3">On December 28, 2011, the Reporting Person transmitted to the SEC a Form 144 covering the sale of the Issuer's common stock reported on Table I.</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">As of December 28, 2011, Reporting Person also owns options to purchase 85,660 shares of Issuer's common stock.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>Douglas M. Pasquale, By: T. Richard Riney, Attorney-In-Fact</signatureName>
        <signatureDate>2011-12-28</signatureDate>
    </ownerSignature>
</ownershipDocument>
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X0304
4
2011-12-23
0000740260
VENTAS INC
VTR
0001070021
PASQUALE DOUGLAS M
111 SOUTH WACKER DRIVE, SUITE 4800
CHICAGO,
IL
60606
1
0
0
0
Common Stock
2011-12-23
4
S
0
20064
54.6093
D
218745
D
Common Stock
2011-12-27
4
S
0
38486
55.2561
D
180259
D
Common Stock
2011-12-28
4
S
0
200
55.50
D
180059
D
Common Stock
4326
I
By IRA
On December 23, 2011, 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 I. 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 $54.50 to $55.00, 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 (1).
On December 27, 2011, the Reporting Person transmitted to the SEC a Form 144 covering the sale of the Issuer's common stock reported on Table I. 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 $55.00 to $55.55, 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 (2).
On December 28, 2011, the Reporting Person transmitted to the SEC a Form 144 covering the sale of the Issuer's common stock reported on Table I.
These shares are being sold pursuant to a written non-discretionary Rule 10b5-1(c) sales plan dated November 23, 2011.
As of December 28, 2011, Reporting Person also owns options to purchase 85,660 shares of Issuer's common stock.
Douglas M. Pasquale, By: T. Richard Riney, Attorney-In-Fact
2011-12-28