These practice parameters address the diagnosis, treatment, and prevention of conduct disorder in children and adolescents. Voluminous literature addresses the problem from a developmental, epidemiological, and criminological perspective. Properly designed treatment outcome studies of modern psychiatric modalities are rare. Ethnic issues are mentioned but not fully addressed from a clinical perspective. Clinical features of youth with conduct disorder include predominance in males, low socioeconomic status, and familial aggregation. Important continuities to oppositional defiant disorder and antisocial personality disorder have been documented. Extensive comorbidity, especially with other externalizing disorders, depression, and substance abuse, has been documented and has significance for prognosis. Clinically significant subtypes exist according to age of onset, overt or covert conduct problems, and levels of restraint exhibited under stress. To be effective, treatment must be multimodal, address multiple foci, and continue over extensive periods of time. Early treatment and prevention seem to be more effective than later intervention.