Adults with putative attention deficit hyperactivity disorder (ADHD) are increasingly being referred to psychiatric clinics, often following a self-diagnosis, and demanding a prescription for stimulant medication. This has disconcerted many clinicians and started a debate on the appropriateness of this diagnosis in adults (Shaffer, 1994; Lomas, 1995; Diller, 1996) that is reminiscent of the controversies of the childhood diagnosis in previous years (Lancet, 1986). At issue is not only concern about the widespread use of stimulant medication, but also a neurobiological understanding of impulsivity, hyperactivity and antisocial behaviour and the genesis of some psychiatric disorders in adults. How is the validity of this disorder in adults then to be established?