Primary adenocarcinoma arising at a colostomy or ileostomy site is very rare, and only three cases have been reported following surgical treatment of ulcerative colitis. A 38-year-old man who developed an adenocarcinoma originating at the site of a colonic stoma and producing a large fungating tumor mass in the surrounding abdominal wall is described. This occurred 19 years after Miles' operation for a carcinoma of the rectum.