Although malignant sessile colorectal polyps usually require colectomy for proper treatment, the majority of malignant pedunculated polyps can be removed colonoscopically. A polyp is considered malignant if the proliferating cells have penetrated the muscularis mucosa. Total excisional biopsy is necessary to properly assess an adenoma microscopically. Forceps biopsy is inadequate. Virtually all malignant pedunculated polyps can be removed colonoscopically, provided one can reach the lesion, and provided one is experienced with snare electro-surgical techniques. Certain sessile polyps can also be removed colonoscopically, if the lesion is soft and nonulcerated, and if one is familiar with piecemeal polypectomy technique developed by Shinya. If the adenoma is malignant, special attention microscopically must be given to the margin of transection, to the specimen's lymphatics, and to the degree of differentiation of the malignancy. If the margin transection and lymphatics are free of tumor cells, if the malignancy is well differentiated, and if follow-up endoscopic exam reveals no residual or recurrence at the polypectomy site (i.e., Morson criteria), the malignant polyp can be considered cured by colonscopic polypectomy alone. The author's experience with 106 consecutively encountered malignant colorectal polyps over a 10 year period is reviewed. Sixty two lesions were removed by colonscopic polypectomy alone. All patients in this group have done well, except for one patient who had tumor involvement at the margin of polyp transection, who was considered inoperable because of severe medical problems, and who died from hepatic metatases 5 months later. Forty four patients underwent colectomy; 26 of these colectomies were preceded by colonoscopic polypectomy.(ABSTRACT TRUNCATED AT 250 WORDS)