Approximately 1 to 4 percent of children ages nine to 17 years old have conduct disorders. The disorder is more common in boys than in girls. Children and adolescents with conduct disorders often have other psychiatric problems as well that may be a contributing factor to the development of the conduct disorder. The prevalence of conduct disorders has increased over recent decades. Aggressive behavior is the reason for one-third to one-half of the referrals made to child and adolescent Mental Health Disorders services.