Preoperative irradiation has been used to produce tumor regression and allow complete resection of rectal cancer with a sphincter-saving procedure. To evaluate the associated toxicity, the response in the primary tumor, and the postsurgical morbidity in a group of patients with locally advanced rectal cancer treated with preoperative chemoradiation therapy and low anterior resection, 120 patients were treated with 45 Gy of preoperative radiotherapy and a bolus infusion of 5-fluorouracil 450 mg/m2 on days 1 to 5 and 28 to 32 of radiotherapy. Four to six weeks later, 16 lesions were found unresectable; 36 patients underwent abdominoperineal resection or pelvic exenteration, and in the remaining 68 a low anterior resection was performed. For the purpose of this study only the latter group was included. There were 38 men and 30 women, with a mean age of 54.7 ± 13.1 years. Gastrointestinal and hematologic acute toxicity grade 3 to 4 occurred in 12 and 7 patients, respectively. The mean distance of the tumor above the anal verge was 8.2 ± 2.6 cm. In 10 patients the surgical resection included neighboring pelvic organs; 16 patients (23.5%) required a temporary diverting colostomy. The main causes of surgical morbidity were clinical anastomotic leakage in seven (10%), abdominal wall infection in five (7.4%), anastomotic stenosis in three (4.5%), and intraabdominal abscess in one (1.5%). No operative deaths occurred. The postsurgical stages were as follows: no tumor in the specimen, 17 (25%); T1, 4 (6%); T2, 12 (17%); T3, 17 (25%); T4, 5 (7%); any T with N+, 9 (13%); and any T, N with M+, 4 (6%). The median and mean follow-ups were 30.0 months and 37.4 ± 25.0 months, respectively. The local recurrence rate was 2.9%, and the distant recurrence rate was 17%. The administration of preoperative chemoradiation therapy for locally advanced rectal cancer is associated with tolerable toxicity, a high rate of response in the primary tumor that allowed anal sphincter preservation, and a low rate of local recurrence.