The present review addresses the question of whether and how neuropsychological tests assessing cognition in attention-deficit/hyperactivity disorder (ADHD) can contribute to clinical and scientific issues concerning ADHD. Neuropsychological studies have shown various though inconsistent cognitive deficits in patients with ADHD. While patients with ADHD, at group level, may differ from healthy participants in regard to cognitive functioning, there is no distinct psychometric cognitive test or profile allowing an individual diagnosis of ADHD or the identification of subtypes according to DSM. Psychometric neuropsychological tests may provide a precise description of the cognitive problems in individual patients and offer specific information for individualized treatment planning. In addition, neuropsychological assessment may contribute to neuroscientific research by providing endophenotypes or biological markers of ADHD. Cognitive neuropsychological assessment appears to be at present of limited clinical use and confined to individual descriptions.