Attention deficit hyperactivity disorder (ADHD) is a common condition affecting many thousands of children. It is a condition that can have adverse health, social and educational outcomes. It also exacts significant societal costs, economically and socially. This paper hypothesises that the population of children receiving a clinical diagnosis of ADHD is aetiologically heterogeneous: that within this population, there is a group for whom the development of ADHD is largely genetically driven, and another who have a ‘phenocopy’ of ADHD as a result of very adverse early childhood experiences, with the prevalence of this phenocopy being heavily skewed towards populations living with poverty and violence. A third group will have a high genetic risk and have been exposed to violence. These groups will overlap, with epigenetic phenomena and other environmental factors, for example, preterm birth, poor intrauterine growth, foetal exposure to teratogens, playing an important role for all...]]>