Attention deficit hyperactivity disorder (ADHD) is the term most widely used to cover a group of common, chronic neurodevelopmental disorders characterised by developmentally abnormal and disabling levels of restlessness and overactivity (usually combined with impulsiveness) and/or inattention. ADHD is multifactorial in origin, with a strong genetic component and is four times more common in boys than girls. The prevalence of ADHD is at least 5% and that of the most severe form i.e. hyperkinetic disorder (HKD) 1-2%. However, a survey of services for ADHD in Scotland found that only 0.6% of children and adolescents were receiving treatment. [With external links to the evidence base]