Sleep-related breathing disorders require special attention in children who spend a considerable time sleeping. Obstructive sleep apnea syndrome is characterized by episodes of upper airway obstruction during sleep. Symptoms include hyperactivity, enuresis, headache, failure to thrive, and increased respiratory effort and total sleep time. The most common cause is adenotonsillar hypertrophy. Coexisting diseases are obesity, neuromuscular and craniofacial anomalies, and Down's syndrome. Early diagnosis is important to minimize neurocognitive, cardiac and developmental complications.