Editorial. Preface. Abstract. 1. Introduction. 2. Case histories of major accidents in radiotherapy. 3. Clinical consequences of radiotherapy accidents. 4. Causes of and factors contributing to accidents in radiotherapy. 5. Recommendations for the prevention of accidents in radiotherapy. Appendix A : Uncertainty in radiotherapy. Appendix B : Quality audits of the calibration of radiotherapy beams. Appendix C : Case histories of accidents related to decommissioning of radiotherapy equipment and sources.