Children and adolescents with Conduct Disorder tend to be excessively aggressive to people and animals, with problems involving the destruction of property, deceitfulness or theft, and serious violation of rules. They often bully, threaten and intimidate others, start physical fights or use weapons to cause serious harm to others. They tend to steal while confronting a victim into sexual activity. They may have destroyed property or engaged in fire lighting. Sometimes, such children are fascinated by flames and matches. Other children with Conduct Disorder are more likely to have engaged in such activities but without confrontation. They also tend to break rules more regularly, to stay out at night, to run away and play truant from school.

As with ODD, research suggests that there are two broad groups of people with Conduct Disorder. Firstly, a group whose problems start in childhood, develop significant difficulties before age 10 and are more likely to have difficulties persisting throughout life. Less common are those in the adolescent onset group, occurring after 10 years of age and often having difficulties limited to adolescence. Most, but not all, children and adolescents with Conduct Disorder have associated ADHD (more than 90%), and Oppositional Defiant Disorder, especially those with early onset.

Apart from the early age of onset, other features of such children can also include being particularly callous and unemotional, having interpersonal problems such as the absence of empathy, problems in long-term relationships. They may have a superficial charm, but with little show of emotion and a lack of conscience. While some such children are engaged in overt anti-social activities such as fighting and causing physical harm, others are more involved in covert activities such as stealing. Being a core ADHD feature, this group may be more amenable to help.

The very nature of the condition, as the symptoms develop further, makes it hard for the adolescent to co-operate with suggested treatment. There may be trouble with anti-social difficulties, involvement with the police, and the drug and alcohol abuse may make management more complicated. However, even at this stage, effective management is possible with a combination of medical and social interventions, provided the child or adolescent can be encouraged to see that there is something can be done to help him. Individuals, however, are always responsible for their own actions, even if there is an underlying medical condition, and ADHD must not be considered as an excuse, rather as a mitigating explanation and should alert professionals to the need for effective management.