Histopathological studies were performed in 18 dialysis patients with renal cell carcinoma. All patients were classified as stage I according to the criteria in the protocol of Robson. The 2 main cell types in these patients were granular (50%) and clear (44%) cell tumors. Thirty-nine percent of the carcinomas exhibited a predominantly acinar growth pattern, 27% had a papillary, and 17% exhibited a cystic growth pattern. In 28 nondialysis patients, the commonest cell type was clear cell carcinoma (67%) and acinar growth pattern was the predominant one (67%). The incidence of papillary renal cell tumors in dialysis patients was significantly higher than in nondialysis patients (p < 0.05). Patients with papillary renal cell tumors had received longer duration of dialysis therapy than those with nonpapillary renal cell carcinomas (p < 0.05). Seven (39%) showed grade 1 carcinoma and 11 (61%) showed grade 2, but grade 3 carcinoma was not observed. In these patients, 8 had associated acquired cystic disease of the kidney (ACDK). The duration of dialysis in the patients with ACDK was significantly longer (p < 0.001). The most frequent cell type was granular-cell carcinoma (63%) in the patients with ACDK. Six patients without ACDK (60%) showed clear-cell carcinoma and 4 (40%) had granular cell tumors. Seventy-four percent of carcinomas exhibited a predominantly either papillary or cystic growth pattern in the patients with ACDK. However, renal cell carcinomas in dialysis patients with or without ACDK did not show significant differences in growth pattern.(ABSTRACT TRUNCATED AT 250 WORDS)