PDD-NOS is often incorrectly referred to as simply PDD. PDD-NOS is a diagnosis while the term "PDD" or Pervasive Developmental Disorder refers to the class of conditions to which autism belongs. PDD is not itself a diagnosis. There are no specific guidelines for this diagnosis which presents problems for research on this condition.

Characteristics include:

Similar symptoms of ASD involving social interactions, communication and repetitive behaviors, which may vary widely. Some children or adults may not talk and some may talk a lot.

Individuals with this diagnosis do not fit the full criteria of the other spectrum disorders.

Symptoms are usually milder than autism/autistic disorder. It is considered a "catch-all category" between Autism Disorder and Asperger's.