Autism spectrum disorders (ASDs) are a class of neurodevelopmental disorders defined by qualitative impairments in social functioning and communication, often accompanied by repetitive and stereotyped patterns of behavior and interests. The term 'ASD' encompasses autism, pervasive developmental disorder not otherwise specified, and Asperger's syndrome. ASDs show etiologic heterogeneity, and there is no definitive medical test or cure for these conditions. Around 1 in 150 children have an ASD, with males being affected three to four times more frequently than females. The age at diagnosis of ASD ranges from 3 to 6 years, but there is increasing evidence that diagnosis in the second year of life is possible in some children. Early diagnosis will lead to earlier behavior-based intervention, which is associated with improvements in core areas, such as social functioning and communication. Early detection of-and intervention to treat-ASD is crucial because it is likely to lead to an improved outcome.