Professor Peter Theodore Clayton is currently a Professorial Research Associate in the UCL Great Ormond Street Institute of Child Health where he supervises diagnostic tests for inborn errors of cholesterol and bile acid synthesis and, together with Dr Philippa Mills, disorders affecting vitamin B6 metabolism. The Clayton-Mills team is also actively involved in research into these disorders. Previous appointments include Professor of Paediatric Metabolic Disease and Hepatology at the ICH, Consultant in Paediatric Metabolic Medicine at Great Ormond Street Hospital, Member of Council of the British Inherited Metabolic Disease Group and Chairman of the international Society for the Study of Inborn Errors of Metabolism (SSIEM). Most areas of Prof Clayton’s research have involved the use of mass spectrometry to investigate samples from children with unusual clinical presentations. Most cited publications are those on the discovery of, and treatment of, inborn errors of bile acid synthesis, inborn errors of monoamine neurotransmitter synthesis, an inborn error of fatty acid oxidation, inborn errors of manganese homeostasis and disorders affecting vitamin B6 metabolism. For this latter area both Prof Clayton and Prof Mills were separately awarded the international Horst Bickel Prize. In 2018 Prof Clayton was invited to deliver the Komrower Lecture at the Annual Symposium of the SSIEM. Scopus lists 259 publications with 13,540 citations and an h-index of 67.