ABSTRACT. The relationship between attention-deficit hyperactivity disorder (ADHD) and sleep is a complex one that poses many challenges in clinical practice. Recent studies have helped to elucidate the nature of the brain mechanisms and neuromodulator systems underlying the theoretical associations among sleepiness, arousal, and attention. Studies of sleep disturbances in children with academic and behavioral problems have also underscored the role that primary sleep disorders such as obstructive sleep apnea hypopnea syndrome play in the clinical presentation of symptoms of inattention and behavioral dysregulation. In addition, new methodologies used in examining sleep and sleep patterns in children diagnosed with ADHD have shed further light on the prevalence, type, risk factors for, and impact of sleep disturbances in these children. The following discussion of the multilevel relationships among sleep quality and quantity, neurobehavioral functioning, and the clinical syndrome of ADHD expands on previous reviews of the literature and synthesizes what is currently known about the interaction of sleep and attention/arousal in children to propose possible underlying mechanisms, integrate more recent findings, and highlight important areas for future study. In addition, guidelines are provided for a clinical approach to evaluation and management of children with ADHD and sleep problems.