The aim of the present study was to describe the prevalence and associated factors of pervasive developmental disorders (PDD), including autistic disorder and PDD not otherwise specified (NOS), in a clinical sample of 126 children and adolescents (75 males, 51 females; age range 4-18y, mean 8y 8mo, SD 3y 8mo) with tetraplegic, hemiplegic, diplegic, dyskinetic, or mixed types of cerebral palsy (CP); 28% could not crawl or walk even with support, 29% could move with support, and 43% walked independently. Participants were examined for PDD in two stages. In the first stage, probable participants were determined by direct observation, Autism Behavior Checklist score, and medical reports. In the second stage, those with 'probable' symptoms underwent psychiatric examination and their autistic symptoms were scored on the Childhood Autism Rating Scale. The final diagnosis of autistic disorder or PDD-NOS was given according to DSM-IV criteria. Fourteen (11%) and five (4%) of the participants met the criteria for autistic disorder and PDD-NOS respectively. Children with CP and PDD differed from those without PDD in terms of type of CP (p=0.02), presence of epilepsy (p < 0.001), intellectual level (p < 0.001), and level of speech (p < 0.001). PDD was more common in children with tetraplegic, mixed, and hemiplegic CP, and in children with epilepsy, learning disability,* and low level of speech. The findings corroborate the notion that CP is a complex disorder, often associated with additional impairments. PDD is not rare in CP and should be considered in patients with comorbid conditions such as epilepsy, learning disability, and language delay and in the presence of tetraplegic, mixed, and hemiplegic CP types.