DEVELOPMENTAL NEUROPSYCHOLOGY, 27(3), 307-310 Copyright © 2005, Lawrence Erlbaum Associates, Inc. The Neuropsychology of Autistic Spectrum Disorders Natacha Akshoomoff Department of Psychiatry University of California, San Diego Child and Adolescent Services Research Center Children's Hospital, San Diego This special issue represents the work from several of the leading autism research groups in the United States. The studies include behavioral, neuropsychological, and neuroimaging investigations of preschoolers, school-age children, adoles- cents, and adults with an autistic spectrum disorder diagnosis. The Diagnostic and Statistical Manual of Mental Disorders (4th ed., text revision; American Psychiat- ric Association, 2000) includes autistic disorder, Asperger's disorder, and perva- sive developmental disorder-not otherwise specified (PDD-NOS) under the um- brella term pervasive developmental disorders (ASD), but many researchers and clinicians now prefer the term autistic spectrum disorders. Under this term, au- tism is seen as part of a spectrum of disorders that have significant social deficits and the presence of repetitive behaviors and restricted interests in common (Lord & Bailey, 2002; Tanguay, 2004; Wing, 1996). Structural brain imaging studies have revealed neuroanatomical abnormalities in a wide variety of brain regions in children and adults with autism including the corpus callosum, cerebellar vermal lobules V I - V I I , amygdala and hippocam- pus (for review, see Akshoomoff, Pierce, & Courchesne, 2002). Recent studies (Akshoomoff et al., 2004; Courchesne et al., 2001; Sparks et al., 2002) have demonstrated that brain volume is abnormally large in 2- to 4-year-olds who are later confirmed to have a diagnosis of autistic disorder or P D D - N O S . Infant head circumference measurements from children diagnosed with autism or P D D - N O S suggest that the process of early brain overgrowth begins to occur by Requests for reprints should be sent to Natacha Akshoomoff, Child and Adolescent Services Research Center, 3020 Children's Way M C 5033, San Diego, C A 92123^1282. E-mail: natacha@ucsd.edu