This lecture is given in memory of one of our radiological pioneers--Robert Knox. A Scot, born in 1868, he studied medicine in Edinburgh and Guy's Hospital. He was elected to the staff of King's College Hospital, The Royal Northern Hospital, the Royal Marsden Hospital and the Chelsea Hospital for women. He was President of the Roentgen Society and Editor of the British Journal of Radiology for 13 years. His magnum opus was on X-ray diagnosis and Therapy, first published in 1915. He died in 1928, and was one of the great figures in British radiology in the earliest days of our developing specialties. Diagnostic Radiology has changed enormously since 1895, and this change has never been more evident than in the last two decades. With change have come challenges, of new technology, new skills, new demands and new hazards. We share some of these hazards with our colleagues in other medical specialties, and especially the hazard of medical litigation. This is not only a time of prodigious medical advancement, but also a time of increasing litigation. Professor Sir Malcolm McNaughton has suggested that the increase in negligence claims is paradoxically due to better medical care. Improved skills and the success of modern technology have given patients a far greater expectation of medical care, and when that skill fails, they turn to litigation (McNaughton, 1987). For all specialties the claims handled by the Medical Defence Union (MDU) numbered 49 in 1947 and almost doubled to 92 in 1957. At the Medical Protection Society (MPS), in the Cases Committee alone, we now listen to approximately 80 cases per month and these are only the expensive cases which are complicated legally or involve issues of professional principle that require safeguarding. When assessing these figures it should be noted that the number of doctors in the United Kingdom has greatly increased since 1947 and the membership of both the MPS and the MDU has increased correspondingly. Not all medico legal problems concern claims. There are many issues, such as complaints not amounting to negligence, coroners inquests, matters relating to standards of care, ethical behaviour, and contractual obligations. The increase in written requests from hospital practitioners for the period 1983 to 1987 is illustrated in Table 1. In Table 2 the incidence of litigation is related to specialties between 1983 and 1986. The table includes claims in each speciality and requests for help in other legal issues. Obstetrics and gynaecology lead the table, followed by general surgery, orthopaedics and accident and emergency. Radiology is well down this league table, but this is not the case in the United States of America, where it now lies in third place (Table 3). Viscount Hanworth speaking in the House of Lords on 'Damages against the Medical Profession' said, 'It appears that anything done in America, sooner or later crosses the Atlantic to England, sometimes after the Americans themselves have realised their mistakes or found a better solution. Despite warnings from others and myself, it would appear that damages against our medical profession are rising and that we are in danger of Table 1 UK members (Medical and Dental personnel) requesting help with medico-legal problems (in thousands)