Autopsy reports on 155 successive end-stage renal disease (ESRD) patients and 147 control patients without ESRD, matched for age, race and gender, were collected. Cystic transformation of the kidneys was noted in 58% of the ESRD patients and 13.6% of the control patients. There were 25 ESRD patients with renal adenoma and 3 with renal cell carcinoma. The single best predictor of cystic transformation or tumorous degeneration was patient’s age. A statistically significant association between cystic transformation and gender, as well as the cause of ESRD, was also found. In contrast to previous reports we were unable to document a strong association between the incidence of either cystic transformation or tumorous degeneration with the duration of dialysis, nor did these two parameters correlate with mode of dialysis. We suggest that cystic transformation of the kidneys in ESRD is related to age and renal failure per se, is not strongly associated with duration of dialysis and is independent of mode of dialysis. Concomitant tumorous degeneration was frequent, but this was usually an incidental autopsy finding. Renal malignancy was uncommon and metastases were absen