Attention deficit hyperactivity disorder (ADHD) affects a significant portion of the population--some 5% of all school-aged children--and approximately half of these individuals continue to show the full disorder in adulthood. Recent studies point to a strong genetic component in the etiology of this disorder. Questions have been raised as to the relatively high prevalence of this condition in the population, given its apparent maladaptive nature in present-day society. In this article, we review and discuss three theories regarding the possible adaptive function of ADHD: the hunter, fighter, and wader theories. Although no theory entirely explains the occurrence of ADHD, it is worthwhile to note that, at least historically, ADHD may have served an adaptive function and may have been selected by the environment for survival.