He was born at Hampstead on 14 February 1875, son of John Howard Mummery FRCS (1847-1926) and Mary Lily, his first wife, daughter of W Lockhart of Shanghai. John Howard Mummery (for a memoir of whom see *Plarr's Lives* 2, 81 and *British dental Journal* 1926, 47, 1023-7) was a prominent dental surgeon in London and had been President of the Odontological Society; he was elected a Fellow of the College in 1923 as a Member of 20 years' standing. His father, John R Mummery, had also been a dentist, but made his mark as an anthropologist. J P L Mummery's younger brother Stanley Parkes Mummery (1878-1945) MRCS also distinguished himself as a dental surgeon. John Percy Lockhart Mummery (in later life he hyphenated the double surname) was educated at the Leys School and Caius College, Cambridge, where he took second-class honours in the first part of the Natural Sciences Tripos in 1897. He was appointed an assistant demonstrator of anatomy at Cambridge. Mummery took his clinical training at St George's Hospital, qualifying in 1899 and proceeding to the Fellowship in 1900 after holding resident posts at St George's, and winning the Thompson gold medal there. He also worked at the North Eastern (now Queen Elizabeth) Hospital for Children at Hackney and at King Edward VII Hospital for Officers, but he really found his métier when he was appointed to the staff of St Mark's Hospital for Diseases of the Rectum in 1903. He became senior surgeon on the retirement of Swinford Edwards in 1913 and was made emeritus surgeon when he himself retired in 1935; in 1940 he was appointed consulting surgeon and a vice-president. Lockhart-Mummery not only made a great career for himself, becoming probably the best-known proctologist in London, but he raised St Mark's from being a small institution into the front rank of special hospitals. His work is recorded in the *Collected Papers* published to celebrate the centenary of St Mark's in 1935. Lockhart-Mummery was a Hunterian professor at the College in 1904, lecturing on the physiology and treatment of surgical shock and collapse. The small book which he based on this lecture, *The after-treatment of operations* (1903), was extremely successful, running to four editions and being translated into several languages including Arabic. He won the Jacksonian Prize for 1908 with his essay on diseases of the colon, which he published and subsequently enlarged as *Diseases of the Rectum and Colon* 1923, second edition 1934. He was the first secretary and moving spirit of the British Proctological Society in 1913, and saw it become a section of the Royal Society of Medicine in 1939, and became its President. He was also President of the section of proctology at the British Medical Association's annual meeting at Newcastle in 1921, and of the section of children's diseases in the Royal Society of Medicine. Lockhart-Mummery was one of the founders of the British Empire Cancer Campaign, first chairman of its executive committee, and active in its work till the end of his life. He was prominent in promoting the London International Cancer Conference of 1928, was much interested in heredity in cancer and a pioneer of the study of familial polyposis (1925). He published a semi-popular book on the *Origin of Cancer* in 1932, and two collections of fictional essays, *After us* 1936 and *Nothing new under the sun* 1947, the first of which contained an imaginary account of England in AD 2456. He devised an electric sigmoidoscope as early as 1904, while his operation for perineal excision of the rectum (1925) became classical. Lockhart-Mummery was a man of many interests, fond of fishing and a regular player of golf in spite of the handicap of losing a leg while a young man, and, in his old age, of bowls. He was also a keen dog racer, winning the Dog Derby with one of his greyhounds. He married twice: (1) in 1915 Cynthia daughter of R A Gibbons; of the two sons of this marriage, one Hugh Evelyn Lockhart-Mummery FRCS succeeded him at St Mark's Hospital; (2) in 1932 Georgette, daughter of H Polak of Paris. He had practised at 149 Harley Street, but after retirement lived at Hove, where he died on 24 April 1957, aged 82. A Bibliography of his writings is included in the *Collected Papers of St Mark's Hospital* 1935, pages 417-423.