Pervasive Developmental Disorder-Not Otherwise Specified (PDD-NOS) falls under the umbrella of Autism Spectrum Disorders. The DSM-IV criteria specify that if the criteria for classic autism are not met in some way, that this diagnosis may be used. Below is the specific criteria used.
The essential features of PDD-NOS are severe and pervasive impairment in the development of reciprocal social interaction or verbal and nonverbal communication skills; and stereotyped behaviors, interests, and activities. The criteria for Autistic Disorder are not met because of late age onset; atypical and/or sub- threshold symptomotology are present.
This category should be used when there is a severe and pervasive impairment in the development of reciprocal social interaction or verbal and nonverbal communication skills, or when stereotyped behavior, interests, and activities are present, but the criteria are not met for a specific Pervasive Developmental Disorder, Schizophrenia, Schizotypical Personality Disorder, or Avoidant Personality Disorder. For example, this category includes “atypical autism”– presentations that do not meet the criteria for Autistic Disorder because of late age of onset, atypical symptomatology, or sub-threshold symptomatology, or all of these.