The term PDD is not a specific diagnosis; but an unbrella term under Autistic Spectrum Disorder. Said to be a stem of Aspergers Syndrome.
A person is diagnosed as having PDD if he or she has some behaviours that are seen in autism/aspergers syndrome but doesn't meet the full criteria of having typical autism. If a diagnosis of PPD is made rather than autism, it's important that the diagnosis clearly specifys the bahaviours present. It is more useful if specific behaviours are noted down on reports made by various people rather than discriptions of vague general terms. The treatment of PDD is similar to Autism. As with Autism, early diagnosis and early intervention will help the person to go on to lead a happy productive life.