Objective: In children with ADHD who have comorbid disruptive behavior diagnoses distinctions between oppositional defiant disorder (ODD) and conduct disorder (CD) remain unclear. The authors investigate differences between ODD and CD in a large clinical sample of children with ADHD. Method: Consecutively referred and systematically assessed male children and adolescents with either ADHD (n = 65), ADHD with ODD (n = 85), or ADHD with CD (n = 50) were compared using structured diagnostic interviews and parent, teacher, and clinician rating scales. Results: In children with ADHD, significant differences emerged between ODD and CD in the domains of delinquency, overt aggression, and ADHD symptom severity; ADHD with CD was most severe, followed by ADHD with ODD, and ADHD had the least severe symptoms. Distinctions between ADHD with CD and the other two groups were found for parenting, treatment history, and school variables. Conclusion: Within the limits of a cross-sectional methodology, results support clinically meaningful distinctions between ODD and CD in children with ADHD. (Contains 4 tables.)