Between 1922 and 1934, Moncrieff worked at various positions including the
Middlesex Hospital in London and the
Great Ormond Street Hospital also in London, starting initially as a
resident and later professing to being a medical registrar. and the
Hammersmith Hospital from 1935 to 1964. In 1934, he was appointed to the consultant staff of both the Middlesex Hospital and the Great Ormond Street Hospital as physician. All the appointments were interrupted by the
World War II, when he worked at the Emergency Medical Service. at the
University of London and Director of the institute, a position he held until 1964, which was based across the hospitals,
Queen Elizabeth Hospital for Children, Hackney, the
Royal Postgraduate Medical School, Hammersmith, and at Great Ormond Street. The next few years were spent assisting in the organisation of child health services in
Hertfordshire, where he lived, and in continuing his work on
phenylketonuria, until he suffered a stroke in 1968 and had to drastically reduce his working habits. ==External work==