Chromosome aberrations were determined in short-term cultures of 18 papillary renal cell tumors, as well as in the cell line ACHN, and the results were evaluated together with 20 previously published cases. We found that chromosomes 7, 17, and 16 and the Y chromosome were specifically involved in the karyotype changes in this tumor type. A combination of tri- or tetrasomy 7 and trisomy 17, as the only autosomal karyotype changes, marks benign papillary renal cell adenomas (ten cases). Malignant papillary renal cell carcinomas (29 cases) were characterized by additional trisomies: trisomy 16 occurred in 20 tumors, and trisomy 12 and 20 in 8 tumors each. Loss of the Y chromosome was observed in 7 of 9 benign and in 23 of 25 malignant tumors that developed in males. None of the papillary renal cell adenomas or carcinomas showed a loss of 3p or gain of a 5q segment, both of which are characteristic of common non-papillary renal cell carcinomas.