After briefly analyzing the concept and genesis of dysplasia starting with the normal large bowel cell and then illustrating the polyp-carcinoma sequence, the authors report on their experience with 283 endoscopic polypectomies in a total of 1.875 patients undergoing endoscopy of the rectum, sigmoid and large bowel since 1980. Forty-nine polyps presented severe dysplasia, and 38 had already degenerated to carcinoma; nine of the carcinomas had invaded the stalk and the patients were subjected to resection of the colon and mesocolon, lymph-node metastases being observed in 1 case.