This report presents three cases of colon tumors which developed after an ureterosigmoidostomy. In a checkup, four years after the operation, an inflamed polyp was found in one patient. The second patient developed an adenoma in the section of the colon where the ureter had been implanted. The last patient died of adenocarcinoma of the colon 26 years after her operation. Possible reasons for the development of the tumors, specifically the cancerous ones, are discussed. The risk of developing colon carcinoma is 500 times higher in those who have had an ureterosigmoidostomy than in healthy people. In the case that the ureters are rediverted the section of the colon where they were previously attached must be excised; since there is a strong possibility of cancerous development. To detect the early development of tumors in the colon, we suggest that patients have their stool tested for blood at regular intervals starting 3 years post operatively. If no problems arise barium enema and coloscopy are recommended every five years.