Developmentally inappropriate degrees of hyperactivity, inattention and impulsivity are common symptoms in childhood. If of early onset (before 7 years), present in different settings and to a degree that causes functional impairment, a diagnosis of attention-deficit hyperactivity disorder (ADHD) or ‘hyperkinetic disorder’ should be considered. The age criterion is crucial to distinguish ADHD and hyperkinetic disorder from later-onset conditions such as agitated depression, adolescent-onset socialised conduct disorder (probably not linked to ADHD) or hypomania, that might appear superficially similar. Attention-deficit hyperactivity disorder and hyperkinetic disorder are commonly associated with language, learning and social impairments. Indeed, in severe cases hyperactivity could be a marker of a multifaceted developmental disorder. Hence, competent assessment usually requires a thorough history, often using a number of sources.