Inattention, impulsiveness and hyperactivity are the main clinical features that characterise the attention deficit hyperactivity disorder (ADHD). Children with ADHD essentially present with diurnal manifestations but studies have recently shown a link between sleep and daytime symptoms. ADHD children could present sleep problems such as agitated sleep, sleep-onset difficulties, low arousal threshold during the night. Such sleep difficulties have been shown to occur more frequently in children with severe diurnal ADHD symptoms. Sleep studies using polysomnography have been performed in children with ADHD. Abnormalities during sleep such as increased motricity could be responsible for hypovigilance as measured using multiple sleep latency tests. Prevalence and physiopathology of sleep disorders including awakening mechanisms (micro-arousals, arousal threshold) from sleep yet need to be clarified in ADHD children. Understanding the mechanisms governing the sleep-wake balance seems essential for the comprehension of ADHD. Excessive nocturnal motricity could be the expression of a monoaminergic dysfunctioning previously reported in ADHD and could lead to new therapeutic gateways as well as hypovigilance.