In a series of 772 renal transplant patients, 84 had analgesic nephropathy (AN). Four of them had renal pelvic carcinoma. The incidence of atypical urothelial changes of the renal pelvis was studied in 56 AN patients, the majority nephrectomized before or shortly after the renal transplantation. Urothelial atypia, usually bilaterally, was found in 27 patients. Multiple sections resulted in an even higher incidence (8/9). No atypical changes were found in normal kidneys or in end-stage diseased kidneys with other diseases, or in chronically rejected renal allografts. These findings further strengthen the association between intake of phenacetin-containing analgesics and the development of renal pelvic tumors. Patients with end-stage analgesic nephropathy are a high-risk group for developing urinary tract tumors and should be subjected to endoscopic and cytologic surveillance. After renal transplantation, prophylactic bilateral nephroureterectomy is advocated.