The increased risk of colon carcinoma following urinary diversions via colon makes knowledge about preneoplastic changes necessary. In 30 ureterosigmoidostomy patients with a mean observation period of 16 years flexible sigmoidoscopy with biopsies and nitrosamine analysis of the feces/urine mixture have been performed. In the biopsies we found an increased sialomucin concentration at the ureterocolonic anastomosis in 29.2% - sialomucin is supposed to be a preneoplastic change - with no significant difference to the mucosa periureteral and in the rectum. In 58.3% we found chronic inflammation at the anastomosis, in 29.2% periureteral and 4.2% in the rectum. 2/30 patients developed adenocarcinoma, 1 patient an atypia and 1 patient a juvenile polyp. The nitrosamine excretion of the ureterosigmoidostomy patients were significantly increased compared to 20 healthy controls with no correlation to the histology at the anastomosis or the observation time. Because of the multilocular presence - colon carcinomas develop only at the anastomosis - sialomucin and chronic inflammation seem to be no preneoplastic changes in urinary diversions. The nitrosamine analysis is not suitable for routine follow up as well.