The Medical Research Council (MRC) National Survey of Health and Development (NSHD) is the oldest and longest running of the British birth cohort studies. Also known as the 1946 British birth cohort study, the aims have changed over time. During childhood, the main aim was to investigate how the environment at home and at school affected physical and mental development and educational attainment. During adulthood, the main aim was to investigate how childhood health and development and lifetime social circumstances affected adult health and function. NSHD is now a life course study of ageing.