Multiple lines of evidence indicate that brain enlargement in autism is a real phenomenon. However, the time course and pattern of this enlargement, and the relationship to clinical features, is not yet clear. It will be critically important to examine subjects over time (a longitudinal design) in order to characterize the trajectory of MRI brain development in conditions such as autism. Dr. Hazlett's research team at UNC has developed image processing tools specifically designed for highly-efficient, reliable and valid processing of pediatric MRI data. Their early results from a longitudinal MRI study of brain development demonstrate generalized enlargement of white and gray matter volume in cerebral cortex in autistic individuals at age 2 yrs. This study will track brain development using MRI/DTI scans in 6-10 year olds with autism and controls who have already participated in the longitudinal MRI study of brain development. Forty-two children with autism who have been scanned at ages 2 and 4 will be rescanned at age 6-10. Controls will include typically developing children and a small subset of children with developmental delay. This study will provide more definitive information about the trajectory of brain growth (regions, tissues, structures and fiber tracts) as measured on MRI and DTI. Additionally, Dr. Hazlett will be able to explore behavioral features associated with social cognition and ritualistic repetitive behaviors in an in-depth manner now that the children are older (6-10 years old), which may provide important insights into the development of neurobiological mechanisms and behavioral phenotypes in autism. What this means for people with autism: This study presents a unique opportunity to characterize brain growth from toddlerhood to school-age in individuals with autism. This will reveal the individual trajectory of brain development in autism and allow it to be linked to specific behavioral outcomes.