The specific neurodevelopmental pathways leading to the cognitive and behavioral disturbances in autism are unknown. Several structural brain abnormalities have been associated with autism, and this study will use novel neuroimaging techniques to begin to define meaningful biological sub-divisions of autism. This research will investigate the brain's cortical complexity in same-gender siblings discordant for autism (one sibling has autism and the other does not) as well as in typically developing participants. The sibling study population will allow for greater experimental control of genetic and environmental factors that influence brain development. A novel, whole-brain analysis of cortical complexity will be used to assess the relation between cortical brain shape and autism. The relationship between cortical folding complexity and behavioral features of autistic participants will also be assessed. Comparing these results with a younger sample of children with autism (17-40 months of age) will elucidate the developmental trajectory of cortical folding complexity in autism from the second year of life to 12 years of age. A better understanding of the neurobiological underpinning of autism will allow identification of sub-groups of individuals with autism, leading to the development of more targeted treatments for this disorder.