Attention deficit–hyperactivity disorder (ADHD) in children and adolescents is a common and severe psychiatric disorder with a prevalence between 2 and 6%. In a high percentage of cases, there is a positive family history. In almost all sufferers, persistent functional limitations that impact everyday life are observed. The prognosis for untreated ADHD is very poor, being associated with social decline, drug addiction, and delinquency. Diagnosis is complex. Typical symptoms are often “hidden”. They are age specific and are mainly associated with inattention, impulsiveness associated with aggression and delinquency, and dangerous risk-taking behavior. More than half of patients also have additional comorbid disorders. The treatment concept always includes nonpharmacological interventions, which are often supplemented with drugs.