Successful cytogenetic analysis was performed on 27 samples from 25 patients with RCC, including 7 of 11 tumors studied and 20 cell lines. Clonal chromosomal abnormalities were detected in all 27 samples. The most frequently involved chromosomes were 7, 1, 3, 9, and the Y (20, 17, 17, 14, and 10 cases, respectively). Polysomy 7 or rearrangement of 7q was seen in 80% (20/25) of the patients, and loss or rearrangement of 3p was seen in 48% (12/25); of the latter, four patients had loss of the whole chromosome and 10 patients had deletions or translocations involving 3p, with breakpoints at either 3p11-14 or 3p21-23 (5/7 translocation breakpoints were at 3p21-23). Loss of the sex chromosomes was seen in 15 patients, including -Y in 10/22 males. Other clonal changes included structural abnormalities of chromosome 1 centromere and the long arm, breakpoints at or near the centromere of chromosome 9 (10 patients), polysomy 16, monosomy 17, polysomy 20, and monosomy 22. With the exception of chromosome 3p loss, which was primarily confined to the nonpapillary cases, no specific clonal abnormality was noted for any particular subtype of RCC. Trisomy or tetrasomy 7 and -Y were seen in all subtypes of renal cell carcinoma.