Technically, "Autism Spectrum Disorder" is not a medical term at all, at least not a clinical one, & it should not be used as a diagnosis, as it is merely a descriptive term. A child may be thought to have an ASD, but then would still need further testing to determine which one specifically.
A child who has an ASD will be given a specific diagnosis that is clinically relevant, either Autistic Disorder, Asperger's Syndrome or Pervasive Developmental Disorder-Not Otherwise Specified. The specific diagnostic label that a child is given clinically describes the type of symptoms that a child is expressing at the time of evaluation, not the degree of severity (although it was once that way).
Also, while all Autism Spectrum Disorders are Pervasive Developmental Disorders, not all Pervasive Developmental Disorders are an Autism Spectrum Disorder, even though the two terms are frequently used interchangeably
at 7:33 PM on Jul. 9, 2009