1) A childhood disorder predominately affecting boys and similar to autism (autistic disorder). It is characterized by severe, sustained, clinically significant impairment of social interaction, and restricted repetitive and stereotyped patterns of behavior. In contrast to autism, there are no clinically significant delays in language or cognitive development. (From DSM-IV)

2) Syndrome or disorder usually first diagnosed in childhood, characterized by severe and sustained impairment in social interactions and restricted, repetitive patterns of behaviors, interests, and activities.