It is now 50 years since Leo Kanner first described autism as a distinctive pattern of symptoms in some children with severe developmental problems. Since then the assessment and diagnosis of children with pervasive disorders of development has been refined and much is known about the phenomenology and epidemiology. Autism is a biological disorder of the central nervous system (CNS) of unknown cause. It is associated with a number of organic disorders such as epilepsy and has comorbidity with other psychiatric disorders such as tic disorder. Cognitive abnormalities in social interactions, affect and language are present but there is still debate regarding which of these, if any, is the primary cognitive deficit. Special education and behavioral management has led to modest but important developmental improvement in many children with autism. Autism remains a life-long condition but patterns of symptoms change and skills develop from childhood into adult life.