Attention-deficit hyperactivity disorder (ADHD) is a common developmental neurobiological condition of childhood characterized by age-inappropriate degrees of hyperactivity/impulsivity and inattention to tasks requiring sustained vigilance. Oppositional defiant disorder (ODD) is an externalizing behavior disorder characterized by difficulties with emotional and behavioral regulation that frequently brings the child into conflict with authority figures. In the clinical setting, ODD is the most common ADHD comorbidity. The combination portends more severe symptom severity, daily impairment, and a more at-risk prognosis than either disorder alone. We briefly review the literature on the characteristics and treatment of the ADHD and ODD child. A clinical approach to evaluation and treatment of ADHD and ODD is then presented. This approach emphasizes the importance of child and parent psychoeducation about the two disorders alone and in combination, the importance of behavioral management therapy approaches, the possible need for school and academic supports, and the decision to use evidence-based stimulant or non-stimulant ADHD medications depending on symptom severity combined with child and parental wishes and choice.