Born at Edinburgh on 22 August 1872 the second son of James Paton, a Fellow of the Linnean Society and from 1876 curator of the Glasgow Art Galleries and Museum, and of Mary Kesson, his wife. He was educated at the Glasgow High School and University and at Gonville and Caius College, Cambridge, where he was a scholar. He took first-class honours in the Natural Sciences Tripos, part 1, 1893, and taught botany and physiology at Cambridge before beginning his clinical training at St Mary's Hospital, London in 1897, where he was Shuttleworth scholar. He served as house surgeon to Edmund Owen at St Mary's, 1901, and as demonstrator of anatomy in the Hospital's medical school. He also taught physiology under Sir Thomas M Taylor at Wren's coaching school in Powis Square, Bayswater. He had been particularly interested in botany and worked for a time in Sachs' laboratory at Bonn; but he decided to make his career as an ophthalmologist, and after serving as clinical assistant to Marcus Gunn at Moorfields he was appointed assistant ophthalmic surgeon to St Mary's in 1902, the year in which he took the Fellowship, H E Juler being his senior. In 1907 he became ophthalmologist to the National Hospital in Queen Square, where he gained his special experience in neurological ophthalmology in the last years of Hughlings Jackson's work there. From this double specialization he achieved at the same time, 1929-30, the presidency of the Ophthalmological Society of the United Kingdom and the presidency of the section of neurology at the Royal Society of Medicine, before which he made his presidential address on the classification of optic atrophies. He was also chairman of the Council of British Ophthalmologists. He was secretary in 1909 and president in 1934 of the section of ophthalmology at the British Medical Association's annual meetings. In his earlier years he made several important researches, working with Gordon Holmes on papilloedema and intracranial tumours; and he discovered the syndrome of optic atrophy in one eye with papilloedema in the other, afterwards known as the Foster-Kennedy syndrome (see *Archives of Ophthalmology*, 1942, 28, 704, for admission of Paton's priority). He had also discovered the causative organism of angular conjunctivitis, the Bacillus duplex or Haemophilus diplococcus, but hesitating with Scotch caution to publish prematurely he was anticipated by Victor Morax and Theodor Axenfeld, after whom the organism is usually called the Morax-Axenfeld bacillus. The statement that Paton anticipated Morax and Axenfeld is based on the obituary notices, but as Morax and Axenfeld published their discovery in *Annales d'Oculistique*, 1892, 108, 393, eight years before Paton qualified, his priority is doubtful. Paton exerted a wide influence through the *British Journal of Ophthalmology* of which he was chairman for many years, and also helped in the interbellum decades to resuscitate the International Congress of Ophthalmology, whose successful meetings at Amsterdam 1929, Madrid 1933, and Cairo 1937 owed much to his energy. Although of world-wide reputation he was ever ready to help young workers and took an active interest in current research. He was an excellent and popular teacher, with a soupçon of dogmatism. He retired from St Mary's in 1929 and was elected consulting ophthalmic surgeon and a vice-president of the Hospital. He was elected consulting ophthalmic surgeon to the National Hospital in 1937, in which year he gave the Mackenzie memorial lecture at Glasgow on optic neuritis. He was also ophthalmic surgeon to the Royal Caledonian Asylum, to the Royal Scottish Hospital, and to the Royal Academy of Dramatic Art. He was an honorary member of the French, Japanese, Hungarian, and Spanish-American ophthalmological societies, the Scottish Ophthalmic Club, and the Royal Medical Society of Budapest, and an honorary Fellow of the American Medical Association, the Association for Research in Ophthalmology, and the International Ophthalmic Council. He had a very large private practice, which he carried on at 29 Harley Street till near the end of his life. In later years he suffered from deafness. Paton married in 1906 Mary, daughter of R R Kirkwood of Glasgow, who survived him with two daughters. He died in London after a long illness on 15 May 1943, aged 71. Leslie Paton was a patriotic Scotsman, with a Scottish accent and many of the best racial characteristics. He was a kind-hearted man with a keen sense of humour, cheerful, encouraging, wise, friendly, and of great knowledge. He was a firm believer in the recuperative value of holidays and regularly took six weeks away from all work each summer. He was a keen fisherman and very fond of golf, which he played chiefly at Elie in Fife and at Virginia Water. There he built himself a house, Scotch Corner, on the Wentworth estate, where he annually entertained the competitors for the Paton cup, which he had presented to St Mary's Hospital Medical School. He was tall and of imposing presence. Publications: Intravitreous haemorrhages, with W E Paramore. *Lancet*, 1905, 2, 1248. Optic neuritis in cerebral tumours. *Trans Ophth Soc UK* 1905, 25, 129-162, and 1908, 28, 112-144. Some abnormalities of ocular movements, with J H Jackson. *Lancet*, 1909, 1, 900. A clinical study of optic neuritis in its relationship to intracranial tumours. *Brain*, 1909, 32, 65-91. The localising value of unequal papilloedema. *Brit med J* 1910, 1, 664. The pathology of papilloedema, with G Holmes. *Brain*, 1911, 33, 389-432. Classification of the optic atrophies. President's address, section of neurology, RSM, 9 October 1930. *Proc Roy Soc Med* 1930-31, 24, 25-33. Optic neuritis, retrobulbar and papillary. Mackenzie memorial lecture, 29 October 1937. *Glasg med J* 1937, 128, 245-260.