From 1976 to 1981, 171 patients with stage I endometrial adenocarcinoma (FIGO, 1971) underwent intracavitary radiotherapy alone because of medical contraindications to surgery and external-beam irradiation. The mean age of patients was 71 years, with the majority of patients being in the age group of 70-79 years. The intracavitary therapy consisted of intrauterine insertions of radium implants in three consecutive courses according to the packing method of Heyman. The estimated dose delivered to point A and to point B was 80 and 20 Gy (3500-7000 mg-hr; mean, 5500 mg-hr), respectively. The corrected 5-year survival rate for stage Ia was 76% and for stage Ib 72%. Grade had a profound effect on survival; corrected 5-year survival for G1 was 77%, for G2 68%, and for G3 53%, respectively. The total failure rate was 24% (40/171). Most of the recurrences occurred in the pelvis (35/171): uterus, 22; vagina, 9; rectum, 2; and bladder, 1. One patient had both vaginal and uterine failure and five had distant metastases (four abdominal and one pulmonary). No difference was seen in the failure rates of stage Ia and stage Ib patients. No major complications (necessitating hospital care or delay of treatment) were seen. Our findings suggest that for patients with stage I endometrial cancer who are unfit for surgery, intracavitary low-dose-rate radiation therapy alone is an effective alternative treatment with a low risk of complications.