Local control, survival, and toxicity in patients treated with endocavitary radiation therapy for rectal cancer were evaluated. Thirty-five patients received a total of 20 to 155 Gy in 1 to 5 fractions with 50 kV x-rays through a treatment proctoscope. Twenty-nine of the 35 patients were treated with curative intent. Median follow-up was 102 months. Local control was achieved in 23 of the 29 patients treated curatively and in 3 of the 6 treated palliatively. Local control for patients treated curatively was 76% at 10 years. No local failures occurred after 21 months. For patients treated curatively, survival was 65% at 5 years and 42% at 10 years. Toxicity within 90 days after treatment was observed in 77% of the patients. Toxicity occurring more than 90 days after treatment was observed in 80%, but only 1 patient needed a colostomy, which was for a perforation after the biopsy of a benign ulcer. In conclusion, radiation therapy resulted in a local control rate of 76% at 10 years in curatively treated patients. Although most patients experience toxicity from this treatment, loss of sphincter function is rare.