A lifelong disorder, often referred to as ADHD, characterised by overactive behaviour, short attention span and poor concentration. It is thought to be caused by a minor abnormality that affects the part of the brain that allows us to concentrate and focus on tasks. In some countries, attention deficit disorder is diagnosed in up to a tenth of all children; this may reflect differences in paediatric practice and diagnosis rather than a real variation in prevalence. Behaviour therapy is the main treatment. Those children with severe symptoms of restlessness, short attention span and disturbed behaviour may respond to additional treatment with an amphetamine-like drug such as methylphenidate. These are thought to stimulate the part of the brain that is not working properly. Use of this drug has, however, been controversial. Some children are said to respond to dietary restrictions, but this should be undertaken only under medical supervision.