A combined necropsy and ultrasound study in patients with end-stage renal disease treated exclusively by peritoneal dialysis revealed acquired cystic disease of the kidney (ACDK) in five of 15 necropsies and in one of seven sonograms from living patients. Two benign microscopic adenomas were also found in the first group of patients. No malignant renal tumors or hemorrhagic complications were detected. The cause of the cyst formation is clearly related to chronic renal failure rather than dialysis per se, as one patient had cysts prior to CAPD and seven of 41 patients with end-stage renal disease in the predialysis era were found to have renal cysts on postmortem examination. This study shows that ACDK is not uncommon in patients with chronic renal failure treated by chronic ambulatory peritoneal dialysis.