The aim of this investigation was to study the frequency of urinary tract tumors (UTT) in settlements around the South Morava River and its tributaries where Balkan nephropathy is endemic. For this purpose 659 surgery and autopsy records of patients with UTT were reviewed. The records came from 25 counties and 1279 settlements classified as endemic, hypoendemic and nonendemic. Upper tract urothelial, urinary bladder and kidney tumors were included in the evaluation. A highly significant geographic correlation between Balkan nephropathy and UTT localized in renal pelvis and ureter was noted in the South Morava River valley. These tumors were 57 and 61.8 times more frequent in endemic settlements than in control rural and city populations free of Balkan nephropathy. The frequency of urinary bladder tumors in endemic settlements was also increased compared with the nonendemic villages and large cities, up to 11.9 and 8.5 times, respectively. In endemic settlements, upper urinary tract tumors were five times and tumors of urinary bladder were seven times more frequent in families with Balkan nephropathy than in those without, and up to 224 times more frequent than in the city families. Familial clustering of UTT was also noted. The geographic correlation between Balkan nephropathy and UTT supports the speculation that these disorders share a common etiology.