a behavioral syndrome of neurological dysfunction characterized by impaired reciprocal social interactions, impaired verbal and nonverbal communication, impoverished or diminished imaginative activity, stereotypic movements, and a markedly restricted repertoire of activities and interests relative to age. In DSM-IV-TR, the disorder becomes evident by the age of 3 is designated autistic disorder when diagnosed, and is categorized as a pervasive developmental disorder. It is commonly associated with mental retardation, speech delay, and is apparent in 20 or so individuals of every 10,000. Also known as infantile autism, Kanner's syndrome.