[en] Purpose: To evaluate the results of interstitial radiotherapy of anorectal tumors. Patients and Methods: From 1972 to 1993, one of the authors treated 45 patients by an interstitial implant for anorectal tumors. Of these, 33 patients suffered from primary tumors, 19 from squamous carcinoma, 2 from basaloid carcinoma of the anus and the other 12 from primary adenocarcinoma of the rectum. Of 12 patients treated for local recurrence, 10 had adenocarcinoma and 2 squamous cell carcinoma. Of the 33 patients with primary tumors, 27 received a course of external-beam radiotherapy before the implant. The median follow-up was 35 months. Results: Local response depended on the tumor volume treated. All 21 anal tumors showed complete response, 5 patients developed local recurrence and 4 distant metastases; 3 died from their disease. Of 12 rectal adenocarcinomas, 9 responded completely, 4 patients developed local recurrence and 4 distant metastases; 6 died from their disease. In the last group of 12 patients who were treated for recurrent tumors, 7 responded completely. One patient developed local recurrence and 9 distant metastases, only 4 are alive. Conclusions: A combination of external-beam and interstitial radiotherapy is a relatively simple, non-mutilating, but well-tolerated and very effective method of treatment for early carcinoma of the lower rectum and a nus. (orig.)