Born 7 February 1882 at Cawsand, Cornwall, the second child and eldest son of William Henry Trethowan, grocer, and his wife, *née* Hutchings. He was educated at Devonport High School and at the Plymouth Technical College. He entered Guy's Hospital in 1901, after gaining the junior entrance scholarship, and had a brilliant undergraduate career, culminating with the gold medal at the final MB BS examination at the University of London. He served as house physician to Newton Pitt, was resident medical officer in Bright's ward, the ward set aside for paying patients, 1908-10, and was afterwards appointed resident surgical officer to the same ward. He seems to have been undecided for a time whether he should specialize in medicine or in midwifery, but having been placed in charge of a massage and physical exercise department in the hospital and having taken the FRCS, he was appointed surgeon to the newly constituted orthopaedic department when it was opened in 1912. He received a commission as captain, RAMC(T) on 10 May 1918, and was selected by Sir Robert Jones to serve at the Military Orthopaedic Hospital in Ducane Road, Hammersmith. At the end of the war he was appointed surgeon to the Royal National Orthopaedic Hospital in Great Portland Street, and in October of the same year (1919) he became consulting orthopaedic surgeon to Queen Mary's Hospital for Children, Carshalton. The hospital was then under the control of the Metropolitan Asylums Board, and he was continued in the post when it passed to the London County Council. He married in 1916 Joan Durham Hickson, grand-daughter of Arthur Durham, FRCS, who survived him with two sons. He died whilst on a visit to Stockholm on 12 September 1934, and was buried at Rame, Cornwall. Trethowan was a master of his craft as an operator, more especially in the treatment of difficult fractures and in bone grafting; as a teacher he was stimulating and forceful. Music was a hobby, and he was organist and a member of the Guy's Hospital Choral Society. A large practice and great conscientiousness undermined his health and led to the septic sore throat of which he died. Publications: Simple fractures of the upper and lower limbs, in Sir Robert Jones, *Orthopaedic surgery of injuries*, 1921, 1, 57-89. Treatment of hammer-toe. *Lancet*, 1925, 1, 1257 and 1312. Fracture dislocation of the ankle-joint, in *The Robert Jones Birthday Volume*, 1928, pp 409-421. Orthopaedic surgery, in Choyce's *System of Surgery*, 3rd edition, 1932, 3, 902-1052.