Pervasive developmental disorder not otherwise specified

Pervasive developmental disorder not otherwise specified (PDD-NOS)^[1] is a historic psychiatric diagnosis first defined in 1980 that has since been incorporated into autism spectrum disorder in the DSM-5 (2013).

According to the earlier DSM-IV, PDD-NOS referred to "mild or severe pervasive deficits 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.^[2]

PDD-NOS was one of four disorders collapsed into the diagnosis of autism spectrum disorder in the DSM-5,^[3] and also was one of the five disorders classified as a pervasive developmental disorder (PDD) in the DSM-IV.^[4] The ICD-10 equivalents also became part of its definition of autism spectrum disorder, as of the ICD-11.

PDD-NOS included atypical autism, a diagnosis defined in the ICD-10 for the case that the criteria for autistic disorder were not met because of late age of onset, or atypical symptomatology, or both of these.^[5]

Even though PDD-NOS was considered milder than typical autism, this was not always true. While some characteristics may be milder, others may be more severe.^[6]