Invasive carcinomas in polyps removed during endoscopy are described. Most of them can be treated adequately by polypectomy alone, but some need additional surgical treatment. Incomplete excision, poorly-differentiated carcinoma, and lymphatic invasion are associated with increased risk of residual carcinoma and lymph node metastases, making colorectal resection more attractive; however, in elderly patients and poor-risk patients, the risks of surgery should be balanced against the possible advantage of curative surgery. Rectal polyps may be large but sphincter preservation can usually be achieved by different types of local excision. Recently described flat adenomas may contain carcinoma, but may also be treated by polypectomy using snare or hot biopsy.