Autism is characterized by impaired social behavior and a language, and a restricted range of activities. Genome scans for linkage have been conducted with coincident signal for a few specific regions. Several promising candidate genes are being investigated. Documented neuroanatomical abnormalities include enlarged cerebral volume in early childhood and gray and white matter deviations. Autopsy findings include reduced Purkinje cells in the cerebellum and decreased numbers of neurons in the amygdala. Functional brain imaging studies document abnormalities in social brain circuitry, including the fusiform gyrus, superior temporal sulcus, amygdala, and orbit-frontal regions, as well as atypical patterns of cortical connectivity. © 2009 Elsevier Ltd All rights reserved.