<SUBMISSION>
<ACCESSION-NUMBER>0001441848-10-000022
<TYPE>4
<PUBLIC-DOCUMENT-COUNT>1
<PERIOD>20100421
<FILING-DATE>20100423
<DATE-OF-FILING-DATE-CHANGE>20100423
<ISSUER>
<COMPANY-DATA>
<CONFORMED-NAME>FACET BIOTECH CORP
<CIK>0001441848
<ASSIGNED-SIC>2834
<IRS-NUMBER>263070657
<STATE-OF-INCORPORATION>DE
<FISCAL-YEAR-END>1231
</COMPANY-DATA>
<BUSINESS-ADDRESS>
<STREET1>1500 SEAPORT BLVD.
<CITY>REDWOOD CITY
<STATE>CA
<ZIP>94063
<PHONE>650-454-1000
</BUSINESS-ADDRESS>
<MAIL-ADDRESS>
<STREET1>1500 SEAPORT BLVD.
<CITY>REDWOOD CITY
<STATE>CA
<ZIP>94063
</MAIL-ADDRESS>
<FORMER-COMPANY>
<FORMER-CONFORMED-NAME>Biotech Spinco, Inc.
<DATE-CHANGED>20080804
</FORMER-COMPANY>
</ISSUER>
<REPORTING-OWNER>
<OWNER-DATA>
<CONFORMED-NAME>LYONS GARY A
<CIK>0001123343
<STATE-OF-INCORPORATION>DE
<FISCAL-YEAR-END>1231
</OWNER-DATA>
<FILING-VALUES>
<FORM-TYPE>4
<ACT>34
<FILE-NUMBER>001-34154
<FILM-NUMBER>10766815
</FILING-VALUES>
<MAIL-ADDRESS>
<STREET1>12790 EL CAMINO REAL
<STREET2>C/O NEUROCRINE BIOSCIENCES
<CITY>SAN DIEGO
<STATE>CA
<ZIP>92130
</MAIL-ADDRESS>
</REPORTING-OWNER>
<DOCUMENT>
<TYPE>4
<SEQUENCE>1
<FILENAME>primary_doc.xml
<DESCRIPTION>PRIMARY DOCUMENT
<TEXT>
<XML>
<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0303</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2010-04-21</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0001441848</issuerCik>
        <issuerName>FACET BIOTECH CORP</issuerName>
        <issuerTradingSymbol>FACT</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001123343</rptOwnerCik>
            <rptOwnerName>LYONS GARY A</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O FACET BIOTECH CORPORATION</rptOwnerStreet1>
            <rptOwnerStreet2>1500 SEAPORT BLVD</rptOwnerStreet2>
            <rptOwnerCity>REDWOOD CITY</rptOwnerCity>
            <rptOwnerState>CA</rptOwnerState>
            <rptOwnerZipCode>94063</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>2010-04-21</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>D</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>2500</value>
                    <footnoteId id="F1"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>27</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>0</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
                <value>Stock Option (Right to Buy)</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>6.17</value>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2010-04-21</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>D</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>16667</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>27</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <footnoteId id="F2"/>
            </exerciseDate>
            <expirationDate>
                <value>2016-01-23</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>16667</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>0</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeTransaction>
        <derivativeTransaction>
            <securityTitle>
                <value>Stock Option (Right to Buy)</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>9.56</value>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2010-04-21</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>D</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>5000</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>27</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <footnoteId id="F3"/>
            </exerciseDate>
            <expirationDate>
                <value>2010-05-26</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>5000</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>0</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">These shares were canceled and exchanged for a cash payment of $67,500.00 in accordance with the Agreement and Plan of Merger, dated March 9, 2010, among the issuer, Amber Acquisition Inc. and Abbott Laboratories in connection with the merger of Amber Acquisition Inc. with and into the issuer.</footnote>
        <footnote id="F2">This stock option was canceled and exchanged for a cash payment of $347,173.61 in accordance with the Agreement and Plan of Merger, dated March 9, 2010, among the issuer, Amber Acquisition Inc. and Abbott Laboratories in connection with the merger of Amber Acquisition Inc. with and into the issuer.  The cash payment made with respect to this stock option equals the product of (x) the number of option shares canceled multiplied by (y) the difference between the merger consideration ($27 per share) and the exercise price for this stock option.</footnote>
        <footnote id="F3">This stock option was canceled and exchanged for a cash payment of $87,200.00 in accordance with the Agreement and Plan of Merger, dated March 9, 2010, among the issuer, Amber Acquisition Inc. and Abbott Laboratories in connection with the merger of Amber Acquisition Inc. with and into the issuer.  The cash payment made with respect to this stock option equals the product of (x) the number of option shares canceled multiplied by (y) the difference between the merger consideration ($27 per share) and the exercise price for this stock option.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>/s/ Gary A. Lyons</signatureName>
        <signatureDate>2010-04-21</signatureDate>
    </ownerSignature>
</ownershipDocument>
</XML>
</TEXT>
</DOCUMENT>
</SUBMISSION>
