Also known as 'Atypical autism', PDD-NOS is a diagnosis often considered for children who show some symptoms of autistic disorder, but who do not meet the specific diagnostic criteria for other specific Pervasive developmental Disorders.

It generally encompasses cases where there is marked impairment of social interaction, communication, and/or stereotyped behavior patterns or interest, but when full features for autism or another explicitly defined PDD are not met.

It should be emphasized that this ''sub threshold'' category is thus defined implicitly, that is, no specific guidelines for diagnosis are provided. While deficits in peer relations and unusual sensitivities are typically noted, social skills are less impaired than in classical autism.