This report addresses the role of radiotherapy for treating solid tumors. It is based on a systematic and critical review of the scientific literature, covering close to 1700 published studies, involving more than 700000 patients. The report also compares current practice in radiotherapy with scientific evidence and estimates the cost of radiotherapy. The review of the literature shows there is a fairly solid basis for conclusions about appropriate practices in radiotherapy. There are about 650 studies available which are judged to be of high scientific quality, covering more than half a million patients. This article is a summary of the complete report, which appears as Supplement 6 and 7 of this issue. A third volume, 'Critical Issues in Radiotherapy' is available at SBU.