Abstract Autism spectrum disorders are characterized by impairments in social reciprocity and in the development and use of communication, accompanied by the presence of rigid, repetitive and stereotyped behaviours. The term is now commonly used to describe a range of neurodevelopmental conditions that are likely to differ in underlying aetiology. The primary impairment in social relatedness and reciprocity was once considered a particular characteristic of rare individuals in the population but is now understood as a broad dimension of individual difference that is widely distributed in the general population. Autism is more common than was previously recognized and as many as 1 in 200 children show some features of the disorder. It is well established that autism spectrum disorders are highly heritable but the genetic mechanisms are complex and involve several genes and to date no susceptibility loci have been identified. Progress has been made towards earlier identification and there is an increasing consensus regarding the appropriate educational and therapeutic approaches, although impairments will be lifelong in many cases.