Obstructive sleep apnea syndrome (OSAS) is a common and serious cause of metabolic, cardiovascular, and neurocognitive morbidity in children. Children with OSAS have increased upper airway resistance during sleep due to a combination of soft tissue hypertrophy, craniofacial dysmorphology, neuromuscular weakness, or obesity. Consequently, children with OSAS encounter a combination of oxidative stress, inflammation, autonomic activation, and disruption of sleep homeostasis. The threshold amount of OSAS associated with adverse consequences varies widely among children, depending on genetic and environmental factors. The choice of therapy is predicated on the etiology, severity, and natural history of the increased upper airway resistance.