Summary Since July, 1973, endocavitary irradiation has been used to treat 129 patients with rectal carcinoma. The lesion must be a modified Dukes' A, well-differentiated adenocarcinoma and no more than 5 cm in diameter and within 12 cm of the anal verge. Specialized diagnostic techniques assist with the clinical selection. Specially designed proctoscopes are used to visualize the carcinoma which is treated by a Philips RT-50 contact machine. 11 000–12 000 cGy are delivered in four treatments administered at 2–3 weekly intervals. No systemic side effects have been observed and local morbidity is minimal. This treatment preserves the anal sphincter, and sexual function in male patients. Hospitalization is not required and there is no risk of mortality. Recurrence has been observed in six of 129 patients within 18 months of treatment for known reasons. Two of these six patients have died from disease and a further 25 from other causes. The local control rate is 95.3%. This treatment modality has been offered also to 87 patients for palliation and this has been effectively obtained in 82.7%. This technique is an alternative to surgery in selected cases.