We studied the interrelationship between the Autism Diagnostic Observation Schedule-Generic (ADOS-G), the Autism Diagnostic Interview-Revised (ADI-R) and DSM-IV clinical diagnosis, in a Greek sample of 77 children and adolescents, referred for the assessment of a possible pervasive developmental disorder (PDD) and presenting a wide range of cognitive abilities. The agreement of the ADOS-G and the ADI-R with the clinical diagnosis was estimated as satisfactory and moderate, respectively, while both instruments presented with excellent sensitivity for the diagnosis of autistic disorder along with satisfactory specificity. ADOS-G/ADI-R agreement was estimated as fair. Our results confirm the discriminant validity of ADI-R and ADOS-G in diagnosing pervasive developmental disorders in children and adolescents with a wide range of intellectual abilities.