Bryan Jennett, professor of neurosurgery at the University of Glasgow, devised, with colleagues, two key diagnostic tools – the Glasgow Coma Scale, used throughout the world to assess consciousness, and the Glasgow Outcome Scale, used for patients with head injury. His work led to the defining of persistent vegetative state and the establishment of criteria for brain death. He was born on 1 March 1926 in Twickenham, Middlesex, the son of Robert William Jennett, a civil servant, and Jessie née Loudon. His mother’s family had farmed in Lanarkshire, Scotland, though there was a tradition of medicine. His father, an Irish Protestant, worked in the offices of the Royal Irish Constabulary in Dublin, but after his marriage was transferred to the British Civil Service in London, an option offered after the Troubles of 1916 and the establishment of the Irish Free State. At the start of the Second World War, Jennett was evacuated to rural Scotland, and then to Southport, where he attended George V School. He went on to study medicine at Liverpool, qualifying at the top of his year, in 1949, having been president of the British Medical Students’ Association. During his period in Liverpool, he was influenced towards neurosurgery by the lectures of Lord Cohen of Birkenhead on neurology. A neurosurgical house appointment at the Radcliffe Infirmary, Oxford, with Sir Hugh Cairns and J B Pennybacker was followed by National Service at the Military Hospital, Wheatley, which confirmed him in a career in neurosurgery. At the suggestion of Walpole Lewin, who was responsible for the care of head injuries at the Radcliffe Infirmary, Jennett undertook a study of the incidence and features of epilepsy after blunt head injuries, work which later resulted in his important monograph on the subject (William Heinemann Books, 1962). From Wheatley and Oxford, he went to Cardiff and, in 1957, was appointed senior lecturer at Manchester, a post he held until 1962. During his period he was a Rockefeller travelling fellow at the University of California, Los Angeles (UCLA), with W Eugene Stern. There he carried out experimental work on the effects of brain compression on tentorial herniation and the pupil, from which came two papers. The experience in UCLA introduced him to experimental work and research, and he considered staying on in the States, but in 1962 he was recruited to a combined academic and NHS appointment at Killearn Hospital in the West of Scotland Neurological Unit, Glasgow. There he was influenced by Sir Charles Illingworth, who had established a tradition of clinical surgical research. He published, in 1964, the first of five editions of *An introduction to neurosurgery* (London, Heinemann Medical), a small textbook in which he showed his skill in exposition. In 1968, he was given a chair of neurosurgery and, two years later, moved to the new Institute of Neurological Sciences at the Southern General Hospital, which he made into an outstanding centre of neurosurgical research and education in the UK. British neurosurgery had not been orientated much towards research, especially the laboratory sort for which Jennett had become enthusiastic after his experience in Los Angeles. In his new appointment, he showed a gift for co-operation and for enlisting accomplished scientists from other disciplines. With Murray Harper, he set up a Medical Research Council group on cerebral circulation, which studied the effects of carotid ligation, raised intracranial pressure, the sympathetic nervous system and the effect of anaesthetic agents on cerebral blood flow in primates and humans. He continued his studies of post traumatic epilepsy and greatly advanced the study of the pathology and outcome of head injuries. Together with Graham Teasdale, his successor in the chair, he devised a method of quantifying a head injury by using simple clinical observations. This became the Glasgow Coma Scale, an essential instrument in grading the severity of a brain injury. He and Michael Bond, who later became professor of psychological medicine at Glasgow, also devised a simple categorisation of the outcome of head injuries. Jennett’s studies with Hume Adams on the pathology of fatal head injuries drew attention to neuropathological evidence that these brains showed ischaemic damage, presumably occurring in the period immediately following the injury and, therefore, due, at least in some cases, to avoidable factors. This offered the opportunity of improving the outcome by attending to ventilation and avoiding hypotension in the early period after injury and controlling, if possible, raised intracranial pressure. Another co-operative effort, this time with Fred Plum of Cornell University, New York, led to the separation of a group of patients following severe head injury in which lack of awareness and of willed movement was associated with cycles of waking and sleeping, which they termed ‘vegetative state’, usually, though not always, permanent. Jennett’s special and characteristic contribution to the management of head injuries was to look at the evidence or collect new evidence, rather than rely on general impressions and past assumptions. If this sometimes seemed slightly cold-blooded, it was very successful in his hands and greatly changed the position of this important if somewhat depressing branch of trauma surgery. Management now depended on rational knowledge, rather than hopeful expectancy. In 1981 he published, with Graham Teasdale, *Management of head injuries* (Philadelphia, F A Davis Co. 1981), which incorporated these studies. Comparison of this book with earlier publications on the same subject shows how greatly the study of head injuries had advanced in a decade. Jennett’s later work inclined towards more general ethical, legal or administrative problems. When the development of heart transplantation created a need for organs to be taken from patients whose heart and circulation were still functioning, there developed a desire to redefine the criteria for death. Artificial ventilation of patients with very severe brain injuries produced a group of patients who appeared eventually to have no cerebral activity or cerebral circulation, if they were investigated, and who would die if ventilation were to be stopped, since they could not breathe spontaneously. Their circulation, however, continued as the heart remained beating. Such patients, at the endpoint of an overwhelming injury, provided an indispensable source of material for heart transplants. After much discussion, criteria were laid down which pronounced them to be, in effect, dead and therefore available as organ donors. This translation of a prognosis into a ‘state’ was not accepted by everyone in the profession and there was some unease and agitation about it. Jennett successfully brought his skill in laying out an argument, and in public debate, to bear on the problem. A somewhat similar difficulty arose over patients in the permanent ‘vegetative state’ he had described. They could live for many years in this state, fed by tube but showing no signs of higher mental functions, often to the distress of their relatives. The question arose whether their lives could be terminated by ceasing tube feeding. In the end, a judgement of the House of Lords decided it could. Jennett wrote an extensive study *The vegetative state: medical facts, ethical and legal dilemmas* (Cambridge, Cambridge University Press, 2002), which examined all aspect of this difficult problem. The increasing expense of highly complex medical treatment, its effectiveness and its value for money was the subject of his Rock Carling fellowship and monograph (*High technology medicine: benefits and burdens*, London, The Nuffield Provincial Hospitals Trust, 1984) in which, in his usual clear and even-handed way, he examined all aspects of the subject, admitting its failings, which he tended to attribute to misapplication by doctors, but generally defending it. His intellectual and organisational gifts made him sought-after as an administrator. He was on many committees in the UK, especially those concerned with head injuries, epilepsy, criteria of brain death and allocation of resources. He was dean of the faculty of medicine of Glasgow University from 1981 to 1986, visiting professor to universities in the USA, Canada, Australia and New Zealand, a corresponding member of the American Neurological Association and the American Association of Neurological Surgeons, an honorary member of the Society of Neurological Surgeons in America and the stroke council of the American Heart Association. He was president of the International Society for Technology Assessment in Health Care. Jennett was a small man with great energy. He had a sharp tongue, pen and wit, and could be harshly dismissive of people of whom he had little opinion, which sometimes produced enemies. He married Sheila Pope, a fellow medical student at Liverpool, who became a respiratory physiologist at Glasgow. There were three sons of the marriage and one daughter. He and his wife pursued outdoor activities and he was interested in flora and fauna. He was a keen sailor, owned a series of yachts and did much cruising around the coast of Scotland and England. Though tone deaf, he was a sponsor of musical activities. His daughter became a professional cellist. Jennett died on 26 January 2008, aged 81, from the effects of multiple myeloma.