The possible causes of attention deficit hyperactivity disorder are considered, and the drugs that may be of benefit in treating it. Accurate diagnosis is essential for effective management. This includes the syndrome itself and associated conditions. Theories of causation are discussed. These involve the anatomical substrate but, equally importantly, the role of neurotransmitters; and the use of tests such as positron emission tomography will undoubtedly increase understanding. Genetic factors also play a part. Options for treatment are considered. Evidence supports the effectiveness of stimulant drugs, such as methylphenidate. Among the justifications for such treatment are the excessive strains placed on family relationships by the condition, and the disruption of the child's schooling. It must be carefully planned, and a constant watch kept for adverse effects. These can include difficulty in sleeping, poor appetite, loss of weight and tics. Drugs alone, however, are unlikely to help, and attention must first be given to the situation at home and at school, and how this can be improved. Treatment is often successful, and it can be a rewarding condition to treat.