Short-term cultures from 12 oral squamous cell carcinomas were cytogenetically investigated. A normal karyotype was found in 3 tumors, 2 of which had many nonclonal changes. Clonal chromosome abnormalities were detected in the remaining 9 cases, in 6 of them in the form of 2 or 3 abnormal clones. In 5 cases the different clones were cytogenetically unrelated, suggesting a multiclonal origin. Numerous additional nonclonal changes were present in 4 of the 9 tumors with clonal aberrations. None of the structural aberrations, clonal or nonclonal, were found in more than one case; nor did any of the rearrangements correspond to cancer-associated aberrations known from other tumors. The aberration breakpoints of the present series and of previously reported tongue cancer clustered to bands 1p32, 1p22, 1p11, 1q21, 1q23, 1q25, 1q32, 1q42, 1q44, 2q31, 3p11, 4q35, 7p22, 11p15, 11q13, 12q24, and 17q25.