We report the short- and long-term responses to radiotherapy of 82 classic Kaposi's sarcomas. Doses were prescribed ab initio and no attempt was made to discontinue treatment as soon as shrinkage was observed, as has been recommended by others. More than 50% of the lesions regressed completely and nearly all underwent some regression. Almost all recurrences were detected within 2 years of treatment and virtually all occurred in lesions that had not regressed completely within 2 weeks of radiotherapy. We conclude that classic Kaposi's sarcoma should be treated with sufficient radiotherapy from the beginning to provide long-term control.