A pervasive developmental disorder not otherwise specified (Including atypical autism) (PDD-NOS) is one of the four autistic spectrum disorders in the DSM-5 and also was one of the five disorders classified as a pervasive developmental disorder (PDD) in the DSM-IV. According to the DSM-4, PDD-NOS is a diagnosis that is used for "severe or pervasive impairment in the development of reciprocal social interaction and/or verbal and nonverbal communication skills, or when stereotyped behavior, interests, and/or activities are present, but the criteria are not met for a specific PDD" or for several other disorders. PDD-NOS includes atypical autism, because the criteria for autistic disorder are not met, for instance because of late age of onset, atypical symptomatology, or subthreshold symptomat