Acquired cystic kidney disease (ACKD) is a frequent complication of end-stage renal disease. In about 50% of patients on chronic haemodialysis treatment, secondary cysts are detected by sonography/computed tomography or at autopsy. ACKD is associated with an increased risk for the development of renal neoplasias. Renal adenomas are found in 8.8% of the cases, renal cell carcinomas are observed in 2.9% of the patients. The prevalence of renal cell carcinoma is 5-10 times greater in ACKD than in the general population. Therefore, ACKD should be considered as a precancerous condition carrying an increased risk for the development of renal cell carcinoma. Consequently patients with ACKD need careful and regular clinical observation and monitoring by ultrasound or computed tomography. An increased risk for the development of renal cell carcinoma has also been discussed in autosomal dominant polycystic kidney disease (ADPKD) based on anecdotal observations. A careful analysis of the literature as well as a retrospective examination of 86 necropsies (1951-1985) and 25 nephrectomy specimens with ADPKD revealed only one patient with renal cell carcinoma. With respect to the incidence of renal cell carcinoma and the frequency of ADPKD (1:1000) in the general population, the present data do not permit the conclusion that ADPKD represents a precancerous condition.