This chapter discusses the case of a 67-year-old gentleman with a 3-month history of a change in bowel habit. On digital rectal examination, there was an easily palpable soft mass in the low rectum. A colonoscopy revealed an extensive near circumferential rectal polyp. The bulk of the lesion made assessment difficult and precluded endoscopic removal. Endoscopic biopsies characterized this lesion as a tubulovillous adenoma with evidence of focal high-grade dysplasia (5%). Although clearly an extensive lesion, it was thought to be non-invasive and that local excision by transanal endoscopic microsurgery (TEM) would be preferable to a major resection. At TEM, a large, polypoid tumor was found to extend circumferentially from the distal rectum up to the rectosigmoid junction, with the bulk of disease on the right wall. The options were to treat conservatively with IV antibiotics or to intervene surgically, probably by laparoscopy, wash-out, and defunctioning stoma.