Ivor Glyn Williams, the third son of Josiah Williams, a wholesale grocer, and of Ellen Williams (née Rowlands), was born at Pwllheli, North Wales, on 29 August 1907. He was educated at Pwllheli Grammar School and the University of London, before graduating in 1931 at the Middlesex Hospital where he was successively house physician, house surgeon, obstetric house physician and house surgeon to the ENT department. He recorded his indebtedness at this stage to W Sampson Handley, Gordon Gordon-Taylor, Victor Bonney, Eric Pearce Gould and David Patey. After securing his FRCS in 1936 he decided to specialise in radiotherapy and was appointed assistant radiotherapist to the Meyerstein Institute where he joined BW (later Sir Brian) Windeyer. He soon had the distinction of being awarded a Rockefeller Travelling Scholarship (1938-1939) to study megavoltage radiotherapy which was then in its early stages in the United States. He visited many of the major cancer centres there and developed several lifelong friendships, notably with CD Haagensen of Columbia Medical Center, though he never shared that great man's enthusiasm for radical mastectomy. During the second world war "IG" as he was widely known, worked at the Middlesex and at Mount Vernon Hospital, Northwood, serving both as radiotherapist and general surgeon to the Emergency Medical Service. He and Brian Windeyer, together with Professor (later Sir) Alan Moncrieff, took a particular interest in childhood malignant disease at the Hospital for Sick Children, Great Ormond Street. In 1944 he was appointed consultant radiotherapist to Cardiff Royal Infirmary. By 1947 he was back in London as the first director of the new independent department of radiotherapy at St Bartholomew's Hospital, where he had a large complement of beds widely scattered around the hospital. Despite the disadvantages of such geographical spread, "IG" always regarded this as giving him a unique opportunity to bring his staff into close touch with every medical and surgical unit. He also had charge of the only one million volt X-ray therapy machine, installed as early as 1936 by the generosity of Lady Houston and used uninterruptedly throughout the war. After analysing the early results he extended the techniques for management of advanced rectal and cervical carcinoma, and also for treatment of tumours of the thymus and glomus jugulare. All this was achieved in collaboration with colleagues in many different specialties, leading on to the acquisition of a 15 MV linear accelerator with both X-ray and electron beams for clinical and experimental research. After a collaborative review with Reginald Murley and Michael Curwen of the Bart's breast cancer experience in the 1930s (which included the significantly conservative practice of Sir Geoffrey Keynes), the group had no hesitation in advocating simple surgery with or without radiotherapy. Williams was a notable exponent both of more kindly surgery and radiotherapy, ever ready to spare his patients the ordeal of needless overtreatment and thereby collaborating happily with many surgeons from outside St Bartholomew's. He also made notable contributions with the ophthalmologist, HB Stallard, to the treatment of retinoblastoma. With the recognition that malignant disease was second only to accident as a cause of death in childhood, it was natural for the Hospital for Sick Children to turn to IG Williams when developing treatment facilities. Although he regularly visited and formulated treatment policies with his many paediatric colleagues there, he rightly persuaded them that it would be in the best interests of their young patients to have the radiotherapy at Bart's. His vast experience in this field was shown in his book *Tumours of childhood* (1972). Although an outstanding exponent of his specialty, IG was first and foremost a kindly doctor; his compassionate management of patients, young and old, was a joy to behold. Glyn had a well earned international reputation in paediatric oncology, whilst nationally he had been President of both the British Institute of Radiology in 1956, and of the Radiology Section of the Royal Society of Medicine in 1968. Under his kindly direction his department became ever more highly regarded by a wide range of clinicians in many specialties. He was a quiet man and a rather private person with a delightful sense of humour. He married Dora Hughes in 1936 and they had one daughter and one son. On retiring from his hospital appointments in 1972 he and Dora returned to North Wales, close to his birthplace, where he happily cultivated his garden and enjoyed the companionship of family and friends. During that period he happily survived the elective resection of an aneurysm of the abdominal aorta and a gastric resection for cancer, as well as a succession of Stokes-Adams attacks which were relieved by cardiac pacemaker. When he died suddenly at Pwllheli on 9 June 1989, aged 81, he was survived by his wife and children.