Cedric Keith Simpson (20 July 1907 – 21 July 1985) was an English forensic pathologist. He was Professor of Forensic Medicine in the University of London at Guy's Hospital, Lecturer in Forensic Medicine at the University of Oxford and a founding member and President of the British Association in Forensic Medicine. Simpson became renowned for his post-mortems on high-profile murder cases, including the 1949 Acid Bath Murders committed by John George Haigh and the murder of gangster George Cornell, who was shot dead by Ronnie Kray in 1966.

He pioneered forensic dentistry, and was prominent in alerting physicians and others in 1965 to a previously under-diagnosed form of child abuse that he termed battered baby syndrome (and, from 1967, battered child syndrome). Simpson wrote a standard textbook on forensic science and edited Taylor's Medical Jurisprudence, a basic work of reference of the British medical profession. Forty Years of Murder was Simpson's autobiography and became an international best-seller in the late 1970s. He was London's first forensic pathologist to be recognised by the Home Office, and in 1975 his long public service was recognised with the award of a CBE. Simpson had by then gained the reputation of having performed more post-mortems than any other pathologist in the world.

Keith Simpson was born in 1907 in Brighton, Sussex, where his father was a general practitioner. In August 1924, aged 17, Simpson enrolled at Guy's Hospital Medical School. By the age of 25 he was a teacher in the Pathology Department. In 1934 Simpson was made Supervisor of Medico-legal Post-Mortems and had his first case with Scotland Yard. In 1937 he was appointed Medico-legal advisor to Surrey Constabulary.

In 1947 the student textbook Forensic Medicine, which Simpson wrote during the war, was published. Following the death of Bernard Spilsbury in the same year, Simpson became one of the leading forensic pathologists in Britain, with a string of important cases. In 1950, along with Francis Camps, Donald Teare and Professor Sydney Smith, Simpson formed the Association of Forensic Medicine.

In 1963 he was elected to the Royal College of Pathologists. Two years later, Simpson addressed the annual meeting of the NSPCC and spoke on the topic of 'battered babies'.

In addition to his scientific publications, popular works such as his 1978 autobiography Forty Years of Murder made his name familiar to the public.

He practised medicine from 146 Harley Street and Guy's Hospital.

Simpson was a member of many medical organisations, one of the founders of the British Association in Forensic Medicine, a former president of the Medico-Legal Society, and a member of the council of the Royal College of Pathologists and the Medical Protection Society. He was the only London forensic pathologist to be recognised as a Home Office pathologist and was a member of the Home Office Scientific Advisory Committee. A fellow of the Royal College of Physicians and the Royal College of Pathologists, Simpson received honorary degrees from the universities of Oxford, Edinburgh and Ghent. His long public service was recognised with the award of a CBE in 1975. In June 2012, Simpson was honoured with the installation of a Westminster City Council Green Plaque at his former residence at 1 Weymouth Street, Marylebone.