<?xml version="1.0" encoding="utf-8"?>
<ownershipDocument>
    <schemaVersion>X0201</schemaVersion>

    <documentType>4</documentType>
  <periodOfReport>2003-09-29</periodOfReport>
  <notSubjectToSection16>0</notSubjectToSection16>
    <issuer>
        <issuerCik>0000034408</issuerCik>
        <issuerName>FAMILY DOLLAR STORES INC</issuerName>
        <issuerTradingSymbol>FDO</issuerTradingSymbol>
  </issuer>
  <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001222821</rptOwnerCik>
            <rptOwnerName>BARKUS BRUCE E</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>P.O. BOX 1017</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>CHARLOTTE</rptOwnerCity>
            <rptOwnerState>NC</rptOwnerState>
            <rptOwnerZipCode>28201-1017</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
            <reportingOwnerRelationship>
      <isDirector>0</isDirector>
      <isOfficer>1</isOfficer>
      <isTenPercentOwner>0</isTenPercentOwner>
      <isOther>0</isOther>
      <officerTitle>Senior Vice President</officerTitle>
    </reportingOwnerRelationship>
  </reportingOwner>
  <derivativeTable>
    <derivativeTransaction>
      <securityTitle>
        <value>Employee Stock Option (Right to Buy)</value>
      </securityTitle>
      <conversionOrExercisePrice>
        <value>40.75</value>
      </conversionOrExercisePrice>
      <transactionDate>
        <value>2003-09-29</value>
      </transactionDate>
      <transactionCoding>
        <transactionFormType>4</transactionFormType>
        <transactionCode>A</transactionCode>
        <equitySwapInvolved>0</equitySwapInvolved>
      </transactionCoding>
      <transactionTimeliness>
        <value></value>
      </transactionTimeliness>
      <transactionAmounts>
        <transactionShares>
          <value>60000</value>
        </transactionShares>
        <transactionPricePerShare>
          <value>0</value>
        </transactionPricePerShare>
        <transactionAcquiredDisposedCode>
          <value>A</value>
        </transactionAcquiredDisposedCode>
      </transactionAmounts>
      <exerciseDate>
        <footnoteId id="F1"/>
      </exerciseDate>
      <expirationDate>
        <value>2008-09-28</value>
      </expirationDate>
      <underlyingSecurity>
        <underlyingSecurityTitle>
          <value>Common Stock</value>
        </underlyingSecurityTitle>
        <underlyingSecurityShares>
          <value>60000</value>
        </underlyingSecurityShares>
      </underlyingSecurity>
      <postTransactionAmounts>
        <sharesOwnedFollowingTransaction>
          <value>60000</value>
        </sharesOwnedFollowingTransaction>
      </postTransactionAmounts>
      <ownershipNature>
        <directOrIndirectOwnership>
          <value>D</value>
        </directOrIndirectOwnership>
      </ownershipNature>
    </derivativeTransaction>
  </derivativeTable>
  <footnotes>
    <footnote id="F1">This option was granted on September 29, 2003, under the 1989 Non-Qualified Stock Option Plan, and no portion of the option may be exercised prior to September 29, 2005.  Thereafter, the option is exercisable in cumulative installments of not more than 40% of the number of shares subject to the option after September 28, 2005, 70% after September 28, 2006, and 100% after September 28, 2007.</footnote>
  </footnotes>
  <ownerSignature>
    <signatureName>/s/ George R. Mahoney, Jr., by Power of Attorney</signatureName>
    <signatureDate>2003-10-01</signatureDate>
  </ownerSignature>
</ownershipDocument>

