Obstructive sleep apnea syndrome (OSAS) is a well-known clinical entity in adults but until now it has been less well studied in children. Several studies have shown that the prevalence of pediatric OSAS is high (between 1% and 3%) and its consequences can be serious. Major risk factors for OSAS in children include adeno-tonsillar hypertrophy, neuromuscular disease and syndromes such as Down's or Pierre-Robin's syndrome. Definitive diagnosis is by nocturnal polysomnography while other methods such as cardiorespiratory records and nocturnal pulse oximetry are undoubtedly useful. Adenotonsillectomy plays a major role in the treatment of OSAS. Nasal continuous positive airway pressure is an alternative in children who show poor response to surgical treatment or in those with craniofacial alterations. In a few cases, nocturnal oxygen administration can be useful.