The links between sleep and attention-deficit hyperactivity disorder (ADHD) have been a topic of ongoing research and clinical interest in children over the last three decades and more recently in adults suffering from ADHD. Clinically, psychiatrists are faced with frequent reports of sleep disorders in adults and children with ADHD and conversely, sleep specialists report certain symptoms of ADHD (attention deficits, urge for fidgeting) in patients suffering from primary sleep disorders. Excessive sleepiness is found in ADHD and sleep disorders such as hypersomnia, sleep breathing disorder (SDB), periodic limb movements in sleep (PLMS) and circadian rhythm disorders. This has encouraged authors to suggest a model of ADHD involving a deficit in alertness. The aim of this article is to clarify the pathophysiological rationale for the relationship between sleep/arousal and attention-deficit/hyperactivity disorder and to explore future perspectives in terms of management, treatment and development of research fields.