Journal of Research in Medical Sciences1735-199517420120405Co-morbidity and factor analysis on attention deficit hyperactivity disorder and autism spectrum disorder DSM-IV-derived items71457145ENAhmadGhanizadehResearch Center for Psychiatry and Behavioral Sciences AND Department of Psychiatry, School of Medicine, Shiraz University of Medical Sciences, Shiraz, Iran. ghanizad@sina.tums.ac.ir2011042920120405Background: There is a gap in the literature regarding the extent of possible co-occurrence of attention deficit hyperactivity disorder (ADHD) and pervasive developmental disorders (PDD). This study aimed to investigate co-occurring of ADHD in children with PDD. Materials and Methods: A clinical sample of 68 children with PDD was assessed according to DSM-IV criteria to make ADHD and/ or PDD diagnoses. All the different types of PDD were included. DSM-IV derived criteria for ADHD and PDD were analyzed. An exploratory factor analysis was conducted. Results: the rate of autism, Asperger syndrome, Rett’s disorder, childhood disintegrative disorder and PDD-NOS (not otherwise specified) was 55.4%, 16.9%, 3.1%, 3.1%, 21.5%, respectively. 53.8% of the sample was with ADHD co-morbidity. The rate of ADHD subtypes was 37.1%, 22.9%, and 40.0% for inattentive type, hyperactivity/impulsivity type and combined type, respectively. Conclusion: ADHD and its symptoms highly co-occur with PDD. Meanwhile, the result of factor analysis supports the independence of ADHD and PDD diagnostic criteria.Key words: Prevalence, autism, co-morbidity, factor analysis