Sleep disturbance in children, whether because of poor sleep hygiene or sleep-related breathing disorders, is associated with significant behavioral and neurocognitive deficits. The mechanisms by which sleep disturbance contributes to the daytime manifestations are unclear, although it seems that sleep fragmentation and intermittent hypoxia are important. The long-term outcome for children with untreated diseases leading to sleep disruption is currently unknown. Increased awareness and early identification and treatment of conditions that lead to altered sleep should yield improved neurocognitive outcomes in affected children.