Attention-deficit hyperactivity disorder (ADHD) has severe psychosocial consequences over the whole life course of patients and their families. During childhood and adolescence ADHD needs to be discriminated from other psychiatric or somatic disorders. Clinical diagnosis is met according to the diagnostic criteria by integrating several anamnestic sources and standardised diagnostic means. Diagnosis of comorbid disorders is obligatory due to their high prevalence rates. In some cases successful treatment of a child suffering from ADHD requires the additional diagnosis and treatment of ADHD in further family members.