Professor Sir Nicholas Wald FRS FRCP FMedSciDSc(Med) DSc(Med)UCL honoris causa FFPHFRCOG FBiol FRSB In 1983 Nicholas Wald moved from Oxford University to take up the Chair of Environmental and Preventive Medicine at St Bartholomew’s Hospital Medical College (Barts). In 1991 he was a co-founder of the Wolfson Institute of Preventive Medicine at Barts and became its first Chairman and later Director, a position he occupied until 2013 with one three year interruption. Subsequently he continued with his Professorial post at what, in 1995, had become Barts and The London School of Medicine and Dentistry of Queen Mary University of London. In 2019 he became Professor of Preventive Medicine at University College London (UCL) and a Visiting Professor at St Georges University of London. In 1992the Royal College of Obstetricians and Gynaecologists awarded him Fellowship ad eundem and in2005 UCL awarded him the degree of DSc (Med)honoris causa. In 2019 he was appointed Honorary Consultant and Adjunct Professor at Brown University, USA. In 1994 he became the founding Editor of the Journal of Medical Screening and continues to be Editor. In 2000 he received the Joseph P Kennedy Jr Award for his work showing that a lack of the B vitamin, folic acid, was a cause of the serious birth defects anencephaly and spina bifida and showing that most cases are preventable by increasing folic acid intake. He gave the 2010 Royal Society of Medicine Jephcott Lecture on Nutrition in Prevention and the Royal College of Physicians Croonian Lecture on Conceptual Challenges in Preventive Medicine in 2015. He was elected a Fellow of the Royal Society in 2004, Knighted in 2008 for services to preventive medicine and elected an international member of the US Academy of Medicine in 2019.