A comprehensive current survey of the overall incidence and cost of professional medical liability claims and cases does not exist. Over the past five or six years a number of partial studies and articles have been published but the dissimilarity of the data makes more than a rough correlation of these impossible. The Law Department of the American Medical Association is presently undertaking studies that should aid in broadening our understanding of medical, legal, and insurance aspects of professional medical liability, but these are not as yet available. This is not to say that we are in complete ignorance. We can use the facts that are known and from these draw inferences that are likely to be valid. While they may not be perfect, they can be used as guides to conduct and action. An instance of this process is to be found in a brief study of closed professional liability insurance claim files involving radiation therapy. It is to be emphasized that none of the observations and conclusions are medical in nature; they concern only the legal or insurance aspects of the material available. Approximately 55 per cent of the physicians involved were Diplomates of the American Board of Radiology. Of the 45 per cent who were not Diplomates, 7 per cent specialized in Radiology. Payments to claimants followed an identical ratio. About 23 per cent of the claims involved the treatment of cancer and 66 per cent the treatment of non-malignant conditions. In 10 per cent of the claims the malignant nature of the lesion treated was doubtul. In the group of claims involving nonmalignant conditions, the treament of plantar warts was involved in 27 per cent, of other warts in 25 per cent, dermatitis in 19 per cent, tine a capitis in 10 per cent, and other lesions in 18 per cent. These bare figures prove nothing, but allow us to infer that the insuring of radiologists for radiation therapy liability costs an insurance company approximately as much as similarly insuring physicians who are not Diplomates of the American Board of Radiology. This is probably because the radiologist's experience is offset by his use of higher exposures; he treats more patients with larger doses more often than do other physicians. The treatment of non-malignant conditions seems to present a greater professional liability hazard than treatment of cancer. This would be particularly true in the case of the radiologist whose use of radiation is preponderantly in the field of cancer therapy. In this connection, one may at least wonder as to the implications of the recent National Academy of Sciences Report on radiation effects on the present generation and progeny. Where will the physician stand, legally, who has used radiation in therapeutic dosages for a non-malignant condition on a young parent whose subsequent offspring is defective? Is a mutation involved? If so, was it caused by radiation, and was it the medical radiation rendered by Dr. Doe?