John Stephen MacMahon was born at Cootamundra, New South Wales. His father was a solicitor practising there, but he also had a country property where the animals, the horses especially, fascinated the boy. He was educated at St Patrick's College, Goulburn, and from the very outset had an outstanding scholastic record. In spite of the advice of his father and his teachers to go on to the university he preferred to work on the land, but after two years his father died and he then decided to follow his wishes and so started to study law at Sydney University. He soon gave that up and turned to medicine, and these early hesitations are worthy of record in view of the brilliance of his subsequent career in surgery. MacMahon was among the first clinical students to work at St Vincent's Hospital, but after graduating MB ChM with first class honours in 1926 he became a junior resident at the Royal Prince Alfred Hospital, Sydney, with which he was closely associated for the rest of his life. He had become assistant medical superintendent by 1932 when he was given leave to come to England. He was the first Australian to win the Hallett Prize at the Primary Fellowship that year, and in December 1932 he passed the Final Examination. While in London he was a clinical assistant at St Mark's Hospital and also at St Peter's, and he then proceeded to Vienna to study Bohler's treatment of fractures, and also visited Finsterer's clinic. On his return to Sydney in 1933 he resumed his duties at the Royal Prince Alfred Hospital, had plenty of opportunity to practise the techniques he had seen while abroad, especially in the treatment of fractures, and was admitted to the Fellowship of the Royal Australasian College of Surgeons. In 1937 he was appointed Syme Scholar, and in 1946 he became honorary surgeon to the hospital, a post which he held with distinction till he reached retirement age in 1959 and was then made honorary consulting surgeon. In the later part of his career he specialized in thoracic surgery and for that he will long be remembered in Sydney. He married in 1948 Marie Fagan and thus began a family life which was his chief joy ever afterwards. They had three sons and a daughter, and John, who had been an enthusiastic footballer at school took great delight in watching his children at play. At first acquaintance many found him rather brusque and stand-offish, but on coming to know him better the kindly and more friendly side of his nature became apparent, and it was no doubt the family influence which mellowed him in his later years. He died suddenly, while still fully active in clinical and administrative affairs, on 23 January 1968, to the great distress of his family and friends.