The obstructive sleep apnea syndrome (OSAS) is frequent in infancy and childhood. It is caused by a prolonged upper respiratory airway obstructioon during sleep, and adenotonsillar hypertrophy is the most important cause. OSAS may have an impact on physical and cognitive development, but syntoms in children are subtle and may pass unrecognised. Polysomnography is the gold standard technique for OSAS diagnosis and surgical approach with adenotonsillectomy is the most frequently treatment indicated. Early diagnosis and treatment and adequate follow up are important to prevent physical disturbances secondary to chronic hypoxemia and to avoid cognitive deficits associated with disrupted sleep architecture.