A total of 22 patients with the diagnosis of invasive, resectable, primary adenocarcinoma of the rectum limited to the pelvis were enrolled on a Phase I/II trial of pre-operative radiation therapy+low anterior resection/coloanal anastomosis. By pre-operative assessment, all patients had invasive tumors involving the distal half of the rectum and required an abdominoperineal resection. The median tumor size was 4 cm (1.5-6 cm) and the median distance from the anal verge was 4 cm (3-7 cm). The whole pelvis received 4680 cGy followed by a 360 cGy boost to the primary tumor bed. The median follow-up was 29 months (10-60 months). Of the 21 patients who underwent resection, 10% had a complete pathologic response and 90% were able to successfully undergo a low anterior resection/coloanal anastomosis. The incidence of local failure as a component of failure was crude: 23% and 4-year actuarial: 32%. The 4-year actuarial survival was 61%. No patients experienced Grade 3 or 4 toxicity while receiving radiation therapy, and 6% developed a partial disruption of the anastomosis. Of the patients who underwent a low anterior resection/coloanal anastomosis, 89% had a good or excellent functional result. This technique may be an alternative to an abdominoperineal resection in selected patients. Further follow-up is needed in order to determine if this approach ultimately has similar local control and survival rates as an abdominoperineal resection.