From 1965 through 1980, 193 patients with histologically proven endometrial carcinoma, FIGO-AJC Stage I-III, received preoperative radiation therapy. One hundred forty-two patients had Stage I (G1:41, G2:68, G3:33), 47 Stage II, and 4 Stage III endometrial carcinoma. All patients were treated with preoperative radiation therapy (intracavitary application, external pelvic irradiation or both) followed by total abdominal hysterectomy and bilateral salpingo-oophorectomy (TAH-BSO). They were followed from 3 to 18 years (median, 6.2 years) after the completion of the treatment and none was lost to follow-up. Overall 5-year actuarial disease-free survival was 85%. The interval between the completion of radiation therapy and TAH-BSO ranged from 3 days to 123 days (median, 40 days). Five-year and 10-year survivals were 95% among 65 patients who did not have residual cancer in the hysterectomy specimen compared to 75% and 70%, respectively, among 128 patients who had positive hysterectomy specimens (P less than 0.01). The presence or absence of residual carcinoma in the surgical specimen after preoperative irradiation was the only important prognostic variable. The most significant factors associated with residual cancer cells were the interval from the completion of radiation therapy to TAH-BSO (P less than 0.001) and the method of preoperative irradiation in patients with Stage I Grade 3 and Stage II external pelvic irradiation was less frequently associated with residual cancer than intracavitary applications (P = 0.043). With one exception, all patients who failed had residual cancer in the hysterectomy specimen. The depth of myometrial invasion of residual tumor in the hysterectomy specimen after preoperative irradiation was correlated to the frequency of failures (P = less than 0.05). Failures were distributed equally among the pelvis, para-aortic nodes, and distant sites. Complications of treatment were infrequent (7%) and were mild; no fatal complications were seen. The data suggest an optimal interval for hysterectomy is 29 to 42 days after completion of radiation therapy in unfavorable carcinomas of the endometrium. These patients also benefit from external pelvic irradiation with or without intracavitary applications as this therapy provides the highest probability there will be no residual cancer cells in the surgical specimen.