Severe degrees of inattentive and restless behaviour in childhood are a risk factor for later psychological disorders. They have many causes, but a pattern of severe and pervasive hyperactivity with poor concentration in the absence of affective or psychotic disorders should be recognised as a hyperkinetic syndrome. The syndrome is often associated with developmental delays in abilities such as language and motor control. Powerful short-term treatments are available, but long-term ways of promoting normal personality development need more research.