Five cases of juvenile polyps at the level of a ureterosigmoidostomy are described. One of the juvenile polyps contained an area of adenomatous tissue. The mechanisms that might cause these polyps are discussed. The mechanisms that might cause these polyps are discussed. The presence of adenomatous tissue in one of the patients may be a step of the polyp cancer sequence at the level of ureteral implantation in the colon. The authors make a plea for a call-up and close follow-up of all patients who have a ureterosigmoidostomy.