The iagnostic category pervasive developmental disorders (PDD), as opposed to specific developmental disorders (SDD), refers to a group of five disorders characterized by delays in the development of multiple basic functions including socialization and communication. The most commonly known PDD is (1) Autism, with the remaining identified as (2) Rett syndrome, (3) Childhood disintegrative disorder, (4) Asperger syndrome, and (5) Pervasive Developmental Disorder Not Otherwise Specified (or PDD-NOS).