Oppositional defiant disorder (ODD) is a common clinical problem in children and adolescents. Oppositionality and associated types of aggressive behavior are among the most common referral problems in child psychiatry. Grouped among the disruptive behavior disorders, ODD is frequently comorbid with other psychiatric conditions and often precedes the development of conduct disorder (CD), substance abuse, and severely delinquent behavior. Youth with ODD may also have specific CD behaviors, such as aggression. Although compared with CD there exists a smaller and less sophisticated empirical database for ODD, this parameter draws upon the existing ODD and CD literature to make recommendations regarding diagnosis and treatment of ODD. The etiology of ODD is complex and its development is based on a cumulative risk/protective factor model that combines biological, psychological, and social factors. Recommended treatment is multimodal and extensive, involving individual and family psychotherapeutic approaches, medication, and sociotherapy. Methodologically sound controlled clinical trials are lacking. (Contains 2 tables.)