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

    <schemaVersion>X0304</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2012-01-03</periodOfReport>

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

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001203367</rptOwnerCik>
            <rptOwnerName>LUSTIG MATTHEW J</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>30 ROCKEFELLER PLAZA</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>NEW YORK,</rptOwnerCity>
            <rptOwnerState>NY</rptOwnerState>
            <rptOwnerZipCode>10020</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>2012-01-03</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>S</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>21070658</value>
                    <footnoteId id="F1"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>53.45</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>3700186</value>
                    <footnoteId id="F2"/>
                    <footnoteId id="F3"/>
                    <footnoteId id="F4"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>See Footnote (2) (3) (4)</value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>4848.485</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
    </nonDerivativeTable>

    <footnotes>
        <footnote id="F1">Represents shares of common stock agreed to be sold by the Funds (as defined below), in the aggregate, pursuant to the underwriting agreement, dated January 3, 2012, among Ventas, Inc., a Delaware corporation (the &quot;Issuer&quot;), the Funds and Citigroup Global Markets Inc. which provides for a settlement date of January 9, 2012.</footnote>
        <footnote id="F2">Prometheus Senior Quarters LLC, a Delaware limited liability company (&quot;Prometheus&quot;), Lazard Senior Housing Partners LP, a Delaware limited partnership (&quot;LSHP&quot;), and LSHP Coinvestment Partnership I LP, a Delaware limited partnership (&quot;LSHP Coinvest&quot;, together with Prometheus and LSHP, the &quot;Funds&quot;), collectively, may be deemed to beneficially own 3,700,186 shares of Issuer's common stock (&quot;Common Stock&quot;). The Managing Members of Prometheus are LFSRI II-CADIM Alternative Partnership L.P., LF Strategic Realty Investors II L.P. and LFSRI II Alternative Partnership L.P., each a Delaware limited partnership, and Lazard Freres Real Estate Investors L.L.C., a New York limited liability company (&quot;LFREI&quot;), is the general partner of each such limited partnership. Lazard Senior Housing Partners GP LLC, a Delaware limited liability company (&quot;LSHP GP&quot;), is the general partner of LSHP.</footnote>
        <footnote id="F3">[Continued from previous] LSHP Coinvestment I GP LLC, a Delaware limited liability company (&quot;LSHP Coinvest GP&quot;), is the general partner of LSHP Coinvest. Lazard Alternative Investments LLC, a Delaware limited liability company (&quot;LAI&quot;), is the managing member of each of LFREI, LSHP GP and LSHP Coinvest GP. In his capacity as Managing Director of LAI, Managing Principal of LFREI and Managing Principal and Chief Executive Officer of each of LSHP GP and LSHP Coinvest GP, Mr. Lustig may be deemed to be the beneficial owner of the securities which may be deemed to be beneficially owned by the Funds. Mr. Lustig expressly disclaims beneficial ownership of the securities reported herein, except to the extent of his pecuniary interest therein, if any.</footnote>
        <footnote id="F4">The Form 3 filed by Mr .Lustig on May 16, 2011 contained a typographical error and mistakenly reported that the Funds may be deemed to beneficially own 24,854,060 shares of Common Stock.  The correct number was 24,854,285 shares of Common Stock. Accordingly, the number of shares of Common Stock reported as Mr. Lustig's indirect beneficial ownership on each of his subsequent Form 4 filings prior to this Form 4 was 225 less than the number of shares of Common Stock that Mr. Lustig may have been deemed to beneficially own.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>Matthew J. Lustig, By: T. Richard Riney, Attorney-In-Fact</signatureName>
        <signatureDate>2012-01-05</signatureDate>
    </ownerSignature>
</ownershipDocument>
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X0304
4
2012-01-03
0000740260
VENTAS INC
VTR
0001203367
LUSTIG MATTHEW J
30 ROCKEFELLER PLAZA
NEW YORK,
NY
10020
1
0
0
0
Common Stock
2012-01-03
4
S
0
21070658
53.45
D
3700186
I
See Footnote (2) (3) (4)
Common Stock
4848.485
D
Represents shares of common stock agreed to be sold by the Funds (as defined below), in the aggregate, pursuant to the underwriting agreement, dated January 3, 2012, among Ventas, Inc., a Delaware corporation (the "Issuer"), the Funds and Citigroup Global Markets Inc. which provides for a settlement date of January 9, 2012.
Prometheus Senior Quarters LLC, a Delaware limited liability company ("Prometheus"), Lazard Senior Housing Partners LP, a Delaware limited partnership ("LSHP"), and LSHP Coinvestment Partnership I LP, a Delaware limited partnership ("LSHP Coinvest", together with Prometheus and LSHP, the "Funds"), collectively, may be deemed to beneficially own 3,700,186 shares of Issuer's common stock ("Common Stock"). The Managing Members of Prometheus are LFSRI II-CADIM Alternative Partnership L.P., LF Strategic Realty Investors II L.P. and LFSRI II Alternative Partnership L.P., each a Delaware limited partnership, and Lazard Freres Real Estate Investors L.L.C., a New York limited liability company ("LFREI"), is the general partner of each such limited partnership. Lazard Senior Housing Partners GP LLC, a Delaware limited liability company ("LSHP GP"), is the general partner of LSHP.
[Continued from previous] LSHP Coinvestment I GP LLC, a Delaware limited liability company ("LSHP Coinvest GP"), is the general partner of LSHP Coinvest. Lazard Alternative Investments LLC, a Delaware limited liability company ("LAI"), is the managing member of each of LFREI, LSHP GP and LSHP Coinvest GP. In his capacity as Managing Director of LAI, Managing Principal of LFREI and Managing Principal and Chief Executive Officer of each of LSHP GP and LSHP Coinvest GP, Mr. Lustig may be deemed to be the beneficial owner of the securities which may be deemed to be beneficially owned by the Funds. Mr. Lustig expressly disclaims beneficial ownership of the securities reported herein, except to the extent of his pecuniary interest therein, if any.
The Form 3 filed by Mr .Lustig on May 16, 2011 contained a typographical error and mistakenly reported that the Funds may be deemed to beneficially own 24,854,060 shares of Common Stock.  The correct number was 24,854,285 shares of Common Stock. Accordingly, the number of shares of Common Stock reported as Mr. Lustig's indirect beneficial ownership on each of his subsequent Form 4 filings prior to this Form 4 was 225 less than the number of shares of Common Stock that Mr. Lustig may have been deemed to beneficially own.
Matthew J. Lustig, By: T. Richard Riney, Attorney-In-Fact
2012-01-05