OBJECTIVE The management of rectal tumors is complex, because of the balance between preserving rectoanal function and curing the patient. Transanal endoscopic microsurgery (TEM) is both an effective treatment for benign rectal tumors and early cancers, and a diagnostic tool for determining tumor depth, or for residual tumors of post endoscopic mucosal resection. In the present study, we evaluated the role of TEM in the management of rectal tumors. METHODS Twenty-six patients with rectal tumors underwent TEM from December 2000 through March 2005 in our department. The operations were performed by a single surgeon, and the indications were mainly limited to a) benign tumors for which endoscopic resection was difficult, b) early cancers that had invaded the submucosa within 500 microm of the muscularis mucosae, c) submucosal tumors, i.e., gastrointestinal stromal tumor, carcinoid tumors, d) local excision for diagnosis, and e) palliative resection for high-risk cases. Anesthesia, operation time, sizes of the tumor and of resected specimens, postoperative complications, length of hospitalization, pathological results, and postoperative recurrence rate were reviewed. RESULTS The mean age of patients was 61.9 years, and the cases included 14 rectal cancers, 7 adenomas, 1 gastrointestinal stromal tumor, and 3 rectal carcinoid tumors. The mean operation time was 96 min (range, 40 approximately 235 min.). The average postoperative hospital stay was 4.8 days. All tumors were resected with horizontal and vertical safety margin. The mean size of the resected specimens was 9.0 cm(2). In one case, the tumor had infiltrated the proper muscle layer, as shown by intraoperative frozen sectioning, which necessitated abdominoperineal resection. In 3 cases, pathological examination revealed massive infiltration into the submucosal layer. 2 patients underwent low anterior resection, and the remaining patient refused additional surgery despite our recommendation. No deaths occurred. No major postoperative complications were noted. The mean follow-up period was 27.2 months. Only one case of lymph node metastasis was observed, in the left iliac lymph node 3 years after TEM. CONCLUSIONS TEM is a minimally invasive surgical procedure for rectal tumors, which allows the whole depth of the rectal wall to be resected with a safety surgical margin. Although TEM requires technical skill and accurate preoperative diagnosis, the procedure is safe, facilitates accurate diagnosis of tumor depth, and limits the need for additional surgery.