Patients with cancer of the rectum, the end part of the large bowel immediately above the anus, are treated with surgery. When the tumour is deemed to present a high risk of recurrence after surgery, a course of radiotherapy (RT) is administered before the operation. It has been proven in clinical studies that this 'preoperative' radiotherapy improves the outcome in rectal cancer patients. Recently, several studies have investigated the combination of radiotherapy with chemotherapy (CRT) before surgery. In theory, adding chemotherapy enhances the antitumour activity of radiotherapy. This meta-analysis has summarized the results of five studies that compared preoperative RT alone with preoperative CRT in rectal cancer patients. All of these studies were randomized, which means that the decision to administer either RT or CRT was determined by chance (ballot draw). The results of the meta-analysis may be summarized as follows. Compared to RT alone, preoperative CRT leads to increased side effects during treatment. Also, postoperative complications are somewhat increased, although the risk of dying from postoperative complications is similar. Preoperative CRT is more effective in causing tumour shrinkage (downstaging), and in preventing local recurrence of the disease. However, addition of chemotherapy did not result in more sphincter preserving surgeries, and did not affect the overall survival in rectal cancer patients.