Delinquent behaviour has its roots in early childhood: Hyperactivity and impulsivity are its precursors, especially if rules are not clearly set in kindergarten and school and if aggressive behaviour is tolerated. Conduct disorders are classified into several subgroups with different treatment strategies. Epidemiologically there is no evidence of an increase of aggression and delinquency in childhood and adolescence. As only a small portion of children and adolescents with aggression and conduct problems are considered to be in need of treatment by their parents, early and intensive intervention is necessary.