Disorders characterized by severe and pervasive impairment in several areas of development: reciprocal social interaction skills, communication skills, communication skills, or the presence of stereotyped behaviour, interests and activities. Autism and Asperger's both fall under the category of PDD as does Rett's disorder, Childhood Disintegrative Disorder and PDD - not otherwise specified (NOS).
Although sometimes incorrectly used to mean PDD-NOS or to avoid telling a parent their child has autism, PDD is not an actual diagnosis but a diagnostic category in the DSM-IV refering to a group of disorders characterized by delays in the development of multiple basic functions including socialization and communication. Symptoms may include communication problems such as using and understanding language; difficulty relating to people, objects, and events; unusual play with toys and other objects; difficulty with changes in routine or familiar surroundings, and repetitive body movements or behavior patterns. Pervasive developmental disorders, sometimes referred to as autistic spectrum disorders (ASD), include: Autistic Disorder, Asperger Syndrome (AS), Rett Syndrome (RS), Childhood Disintegrative Disorder (CDD), and Pervasive Developmental Disorder Not Otherwise Specified (PDD-NOS).