Neoplasia associated with ureterosigmoidostomy is uncommon but important. Two patients, one of whom developed symptoms five years after the ureterosigmoidostomy had been taken down, are reported. The authors support the theory that these tumors may arise from the ureter. When ureterosigmoidostomies are dismantled, the site of implantation should be resected and the patients kept under long-term endoscopic review.