Objective: Compares DSM-IV ADHD subtypes in large samples of 3-to-5 and 6-to-12 year old children with pervasive developmental disorder (PDD) vs. nonPDD clinic referrals. Method: Parents and teachers completed a DSM-IV-referenced rating scale. Results: ADHD subtypes were clearly differentiated from the nonADHD group and showed a differential pattern of co-occurring psychiatric symptoms (more pronounced for teacher--than parent-defined subtypes and older than younger children) that was similar in both PDD and nonPDD samples. The Combined type had more severe oppositional, aggressive, and PDD symptoms than Inattentive type and were from less advantaged homes than other subtypes. Hyperactive-Impulsive type was least impaired. Conclusion: Findings support the notion that ADHD may be a clinically meaningful syndrome in children with PDD.