Conduct disorders are among the most commonly diagnosed mental health disorders in boys and girls, according to the National Mental Health Association. There are four major types of conduct disorder:

• Aggressive conduct. Behavior that causes or threatens physical harm to people or animals.
  
  
• Nonaggressive conduct. Behavior that causes property loss or damage.
  
  
• Deceitfulness or theft. Behavior that involves lying to or manipulating other people or stealing others’ property.
  
  
• Serious violations of rules. Behavior that involves breaking established rules, such as skipping school or staying out past curfew.

In addition, conduct disorders are classified as either childhood-onset type (symptoms appear before age 10) or adolescent-onset type (symptoms appear after age 10). Patients with childhood-onset type tend to be boys who are frequently physically aggressive toward others and who may have poor peer relationships. They may also have a history of other disorders, such as oppositional defiant disorder or attention-deficit hyperactivity disorder (ADHD). The onset of a conduct disorder rarely occurs after age 16.