Cytogenetic study of 30 bladder carcinomas confirmed the heterogeneity and the complexity of the karyotypic picture in this type of tumor. Presence of numerical and/or structural chromosome aberrations was observed in all tumors. Clonal abnormalities were found in 19 cases. Chromosomes most frequently involved in changes were chromosome #1, #3 and #11(36.6%, 26.6%, and 20% of the cases respectively). Trisomy 7 and monosomy 9 were the sole abnormalities in one case each.