Between 1986 and 1990, 16 patients were enrolled in a prospective Phase I/II study of transanal local excision and combined preoperative and postoperative radiation therapy (RT). All patients had biopsy-proven adenocarcinoma extending to within 6 cm of the anal verge and involvement of at least one third of the rectal circumference with tumor. Five of 16 patients (32%) had T3 tumors, and only two patients had T1 tumors. Patients received a single 500 cGy fraction of RT to the pelvis within 24 hours before surgery and underwent transanal excision followed by postoperative RT (median dose, 5040 cGy). With a median follow-up of 33 months, overall 3-year actuarial survival was 94%. Two patients had isolated local recurrences (both successfully salvaged), and four had distant metastases but maintained local control. The 3-year actuarial rates of continuous freedom from any relapse, continuous local control, and no evidence of disease at last follow-up were 53%, 80%, and 71%, respectively. Only three of 16 patients required colostomy, resulting in a 3-year actuarial colostomy-free rate of 77%. There was a trend toward a higher rate of relapse (P = 0.066) in patients with T3 tumors than those with T1 and T2 tumors. Sphincter-preserving therapy for low-lying rectal carcinomas using local excision and combined preoperative and postoperative RT is feasible, although improved local and adjuvant therapy is needed for patients with T3 lesions.