Fifty-seven adenomas containing adenocarcinoma were removed endoscopically from the colons of 56 patients (36 males and 20 females) with a mean age of 64.5 years. The 13 polyps containing carcinoma in situ were satisfactorily treated by endoscopic resection. In 29 cases, the carcinoma had invaded the head, neck or stalk of the polyp. The outcome was good in every case, including one involving invasion of the resection margin. Follow-up or intraoperative studies disclosed the presence of residual lesion in only 4 patients out of 15 with submucosal invasion. All four had invaded resection margins and incomplete endoscopic excision. Endoscopic polypectomy is a suitable therapeutic option for most colonic adenomas containing a carcinoma provided a complete resection is achieved with wide resection margins, particularly in those cases in which the submucosa is not reached.