The findings presented in this study are based on 29.226 autopsies performed (between 1953 and 1977) at Basel University on adult inhabitants of Basel, from which 409 urinary tract tumors (UTT) and 513 phenacetin abusers (PA) were discovered. There were 44 (8.6%) PA with UTT which, when compared with the control group (1.27%), represents a statistically significant increased incidence. Of the 50 UTT in PA, 52% occurred in the bladder, 6% in the ureter, and 42% in the renal pelvis. The induction time for tumors of the urinary bladder was about 27 years, and for tumors of the renal pelvis about 20 years. The commonest tumors arising in PA were invasive solid and non-invasive papillary urothelial carcinomas. PA with UTT died earlier than nonabusers but had metastases as frequently as nonabusers. Analgesic nephropathy was not always an accompanying disease. The daily dose of g/phenacetin in tumor patients in general, and in patients with tumors of the urinary bladder in particular, was about 1 g lower than in patients with analgesic nephropathy (without tumors) and in those with tumors of the renal pelvis. Thus, for the localization of the tumors, the daily dose seems to be more important than the total dose. Our investigation proved that not only tumors of the renal pelvis, but also of the ureter and the urinary bladder, are significantly more frequent in PA than in nonabusers. It is suspected that despite restriction of the over-the-counter sale of phenacetin-containing analgesics and even after stopping any analgesic abuse, UTT will further increase due to the longer induction time. Routine cytological screening tests of the urine are recommended for all known PA. A prescription for all phenacetin- and paracetamol-containing analgesics is necessary.