BACKGROUND Large sessile adenomas of the rectum, with a diameter greater than 5 cm, have a high risk to undergo malignant transformation. Transanal endoscopic microsurgery (TEM) offers an alternative operation method to low-anterior rectum resection in this potentially benign tumor situation. METHODS We retrospectively investigated patients with giant adenomas of the rectum (>5 cm) who were treated by TEM over the last 10 years. A total of 33 patients met the criteria and were analyzed for postoperative complications, histology, and incidence of occult adenocarcinoma; residual tumor status; and tumor recurrence. RESULTS Partial suture-line insufficiency (n=5, 15%) was the major postoperative complication, but could be managed conservatively in four cases. The residual adenoma status was 18% (n=6), especially in patients with tumors sizes more than 30 cm2. In case of adenoma recurrence (n=4, 12%), a conventional transanal excision (Parks) was applicable, as these tumors were mostly located within the suture-line region of the lower rectum. Incidentally, five carcinomas were found in the specimens. In case of advanced tumors (1xpT2, 1xpT3), anterior rectum resection was carried out, whereas for the early tumors (2xpT1 low risk, 1x1 pTis), no further therapy was added. All patients (adenomas and carcinomas, n=33) were without recurrence during follow-up. CONCLUSIONS TEM is an alternative method for the resection of large benign rectal tumors located in the mid- and upper third of the rectum. The main postoperative complication is suture-line insufficiency, which generally heals by conservative treatment.