Forty-two patients with initially unresectable rectal adenocarcinoma were treated with preoperative irradiation and surgery between March 1970 and March 1986 at the University of Florida (Gainesville, FL). No patient received adjuvant chemotherapy. All patients had follow-up for at least 5 years; 23 (55%) had follow-up for 10 years or more. Five patients (12%) underwent an exploratory laparotomy before irradiation; the remaining 37 patients were clinically thought to have unresectable disease. Eighteen patients had tumor fixation to one structure, and 24 patients (57%) had fixation to two or more structures. Lesions that exhibited impaired mobility but not complete fixation were considered to be clinically resectable and are not included in this series. The dose of preoperative irradiation ranged from 3,500 to 6,000 cGy at 180 cGy per fraction; 30 of 42 patients received 4,500 to 5,000 cGy and only 4 patients received less than 4,000 cGy. Forty-one patients were operated on 1 to 11 (mean 4.6) weeks after the completion of radiotherapy; 1 patient died of aspiration pneumonia after completing irradiation but before the planned resection. Resection of the rectal cancer was accomplished in 37 patients. Four patients were found to have extensive unresectable disease at laparotomy. Twenty-one patients had a complete resection: 11 were stage B2, and 10 were stage C2. Twenty patients had incomplete resection due to positive margins (8 patients), distant metastases with or without positive margins (8 patients), or no resection due to extensive disease (4 patients). Two patients died after the operation.(ABSTRACT TRUNCATED AT 250 WORDS)