PDD-NOS is the abbreviation for Pervasive Developmental Disorder Not Otherwise Specified. PDD-NOS and autism are both diagnosed through observation of behaviors, and the diagnosis of PDD-NOS is made when a child has only some deficits or an atypical pattern of deficits. The difference between a diagnosis of autism and PDD-NOS is often very subtle, and people with either diagnosis are likely to benefit from similar approaches to treatment and education.