In 20 patients with colovesical fistulas the origin was sigmoid diverticulitis in 11 and carcinoma in nine. One of the carcinomas originated in the cervix. The first symptom in most was from the urinary tract; nine patients were asymptomatic prior to the formation of the fistula. In only 12 patients was there objective preoperative evidence of the fistula shown by cystoscopy or barium enema examination. The three-stage operation remains the procedure of choice.