Background: Symptoms as in attention deficit hyperactivity disorder (ADHD) are frequent among individuals with pervasive developmental disorders (PDD). The aim of the present study was to examine the impact of inattention, hyperactivity and impulsivity on the clinical phenotype of children and adolescents with PDD. Sampling and Methods: A total of 182 subjects (41 females) diagnosed as having PDD were split into a high (PDD+) and a lower (PDD) attention problem group using the median of the Child Behavior Checklist (CBCL) syndrome scale ‘attention problems’ (median T score = 75). The groups were compared with regard to the degree of coexisting psychopathology, as measured by the remaining 7 CBCL subscales, and autistic core features assessed by the Autism Diagnostic Interview-Revised (ADI-R) and the Autism Diagnostic Observation Schedule using a multivariate analysis of covariance adjusted for age, IQ and socioeconomic status. Results: The PDD+ subjects exhibited a significantly higher degree of general psychopathology than the subjects in the PDD subgroup, regarding both internalizing and externalizing symptoms. In addition, the PDD+ subgroup tended to exhibit more impairments on the social interaction scale of the ADI-R. Conclusions: Clinicians should adjust treatment plans to ensure comprehensive and effective treatment for both PDD and associated ADHD. A dual diagnosis may be essential to the implementation of effective treatments.