Cross-cultural study of childhood psychopathology is an exciting and rapidly developing field. Its primary concern is how cultural factors influence the aetiology, expression, course, outcome and epidemiology of childhood mental disorders. The magnitude of the cultural influences is presumably related to the nature of a disorder. If the disorder is a developmentally inappropriate increase of behaviour with no organic cause, then the variability displayed by this disorder across different cultures is expected to be high. However, even in neurological disorders with a strong biological component, cultural influences can still exert an impact on how the individual and family experience, interpret and respond to the disorder and how society responds to the individual's behaviour. This chapter reviews the cross-cultural aspects of a childhood disorder, hyperactivity, and discusses how cross-cultural data shed light on aiding our understanding the disorder. Hyperactivity refers to an enduring style of behaving in an overactive, inattentive and impulsive fashion (Taylor, 1986). It is a broad behavioural description of children's behaviour and does not carry any aetiological implication. Currently, there are two official diagnostic systems which confer a diagnosis for the disorder – the DSM system (Diagnostic and Statistical Manual of Mental Disorders) of the American Psychiatric Association (APA) and the ICD system (International Classification of Diseases) of the World Health Organization (WHO). Previously the two systems differed in some important aspects, but in their current versions, the ICD-10 and DSM-IV, there is presently more convergence.