<Page>

                                  "EXHIBIT 21"

                               LIST OF SUBSIDIARIES


                Subsidiaries of International Bancshares Corporation

<Table>
<Caption>
        Name                         Business                 % of Ownership
        ----                         --------                 --------------
                                                        
IBC Subsidiary Corporation           Bank Holding Company          100%
IBC Life Insurance Company           Credit Life Insurance         100%
IBC Trading Company                  Export Trading                100%
IBC Capital Corporation              Investments                   100%
IB Capital Trust I                   Capital Securities            100%
IB Capital Trust II                  Capital Securities            100%
IB Capital Trust III                 Capital Securities            100%
IB Capital Trust IV                  Capital Securities            100%
</Table>

                   Subsidiaries of IBC Subsidiary Corporation

<Table>
<Caption>
        Name                         Business                 % of Ownership
        ----                         --------                 --------------
                                                        
International Bank of Commerce       State Bank                    100%
Commerce Bank                        State Bank                    100%
International Bank of Commerce,
  Zapata                             State Bank                    100%
International Bank of Commerce,
  Brownsville                        State Bank                    100%
Gulfstar Group I, Ltd.               Investment and Merchant
                                       Banking                      70%
Gulfstar Group II, Ltd.              Investment Banking             70%
</Table>