Between 1984 and 1992, 27 patients with clinical stage I-II histologically proven adenocarcinoma of the endometrium who had significant medical risks precluding surgery underwent radiotherapy (RT) as the primary treatment. The median age at diagnosis was 74 years. There were 20 patients (74%) with stage I and 7 patients (26%) with stage II disease. Patients were treated with high-dose-rate brachytherapy (HDRB) alone (19/27) or with a combination of external-beam RT and HDRB (2 stage I; 6 stage II). HDRB was delivered using a cobalt-60 HDR remote afterloading unit, with a median dose of 2000 cGy to point A, in two to three fractions given once a week. All HDRB treatments were performed under spinal anesthesia on an outpatient basis. External-beam irradiation to the pelvis was given using 4- to 6-MV photons and a median dose of 4200 cGy was delivered. In all patients, vaginal bleeding was controlled within a few days after completion of RT. With a median follow-up of 47 months, the 8-year disease-specific survival rate was 76%. Patients with stage I had an 8-year survival rate superior to that of patients with stage II (95% vs 21%, P < 0.001). No complications were experienced during HDRB. Late serious complications were seen in 3 patients (11%). Based on this retrospective review, primary RT with HDRB appears to be an effective and safe treatment for those patients with medically inoperable clinical stage I endometrial carcinoma. Because HDRB is given on an outpatient basis, it is an attractive option for these patients. However, in stage II disease the results of treatment are poor and RT alone should be considered only when the surgical risks are too high.