A disturbed cellular DNA content is of potential diagnostic and prognostic relevance in urinary bladder cancer. To evaluate the prognostic significance of individual chromosomal aberrations in superficial bladder cancer, specimens of 105 tumors (67 pTa, 38 pT1) were examined by fluorescence in situ hybridization (FISH). FISH allows quantitation of chromosomes on a cell by cell level. Centromere probes for the chromosomes Y, 1, and 17 were used. There was a strong association between polysomies of the chromosomes 1 (found in 46% of tumors) and 17 (40% of tumors, P < .0001). Polysomies (1 and 17) were significantly more frequent in pT1 than in pTa tumors (P < .0001 each). In pTa tumors, polysomies of both chromosomes were linked to a high risk of recurrences; polysomy 17 was associated with an increased risk of progression (P < .05 each). There was no significant association between polysomies and an unfavorable prognosis in pT1 carcinomas. Previous studies had suggested a prognostic role of Y losses in bladder cancer. However, Y losses were not linked to recurrences or tumor progression in pTa or pT1 tumors of 67 male patients. These data show that marked genetic differences exist between pTa and pT1 carcinomas. They also indicate that polysomies of different chromosomes may have prognostic relevance in pTa urinary bladder cancer.