A prospective study was undertaken to investigate the development of renal cell carcinoma in dialysis patients. Three renal cell carcinomas were detected among 96 hemodialysis patients in 1979, and screening by computed tomographic (CT) scan was continued yearly until 1989. During this 10-year period, one renal cell carcinoma was found in the second year and another in the ninth year. Autopsy performed on seven of 19 patients who died showed one case of small clear cell carcinoma accompanying acquired cystic disease. In 33 males, kidneys were found to have enlarged 2.7 +/- 1.7 times over the 10-year follow-up due to acquired cysts, while no change in kidney volume was noted in 24 females. Native kidneys in nine of 12 patients who maintained functioning grafts were reduced in size. The patient with the largest kidney enlargement (11.5 times) died from retroperitoneal bleeding in 1989. These prospective study results suggest that both the incidence and prevalence of renal cell carcinoma in dialysis patients is high. Furthermore, major complications of acquired renal cystic disease seem to occur predominantly in males.