Pervasive Developmental Disorders (PDD) are characterized by severe and pervasive impairments in several areas of development: reciprocal social interaction skills, communication skills, or the presence of stereotyped behavior, interests, and activities. A diagnosis of autistic disorder is made when an individual displays symptoms across three major areas: social interaction, communication, and behavior. When children display similar behaviors but do not meet the criteria for autistic disorder, they may receive a diagnosis for another category of Pervasive Developmental Disorder.

This section was designed to provide more information about Asperger's Syndrome, Autism, CDD, Retts, Fragile X, PDD-NOS, all of which are types of PDD, and their definitions according to the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSM-IV).