One hundred forty-eight patients were treated with preoperative radiation therapy and surgery for resectable rectal adenocarcinoma at the University of Florida between 1975 and 1986. All patients had at least 5 years' follow-up; no patient was lost to follow-up. Three treatment protocols were used over the study period: 1975 to 1978, 3500 cGy in 20 fractions; 1979 to 1983, 4000 to 5000 cGy at 180 cGy per fraction; and 1984 to 1986, 3000 cGy in 10 fractions. The change was made to 3000 cGy in 10 fractions to reduce the inconvenience and expense associated with preoperative radiation therapy without sacrificing any improvement in local control or complication rates. There were no significant differences in the rates of local control, absolute survival, cause-specific survival, or complications between the three preoperative radiation therapy protocols. The results were compared for the 132 patients who underwent complete resection after preoperative radiation therapy and a series of 135 patients who underwent a complete resection alone for adenocarcinoma of the rectum at the University of Florida between 1959 and 1976. The results at 5 years, calculated by the product-limit method, for preoperative radiation therapy and surgery compared with surgery alone, respectively, were as follows: for local recurrence-free survival, 96% and 67%; for absolute survival, 66% and 40%; and for cause-specific survival, 77% and 50%. All of these differences are significant (p = 0.0001 or less). A subset of 56 patients with locally advanced lesions, based on tethering or circumferential involvement of the rectal lumen, treated with preoperative radiation therapy and surgery were compared with patients treated with surgery alone for stage B2 and C cancers. There was a significant improvement in local control and survival rates in the group irradiated before operation. There was no apparent increase in the incidence of postoperative complications in the patients irradiated before operation.