Provides critical examination of research published during past ten years addressing Conduct Disorder (CD), Attention Deficit Hyperactivity Disorder, Oppositional Defiant Disorder (ODD), and internalizing disorders. Concludes comorbidity varies with age, gender, informant, diagnostic criteria, and nature of the sample. Implications of comorbidity for etiology, diagnosis, treatment, law, and policy, and preventive efforts in work with children and adolescents with CD are offered for school psychologists. (Author/MKA)