The obstructive sleep apnea syndrome (OSAS) is a common and serious condition during childhood. Its pathophysiology remains poorly understood. Although OSAS is related to adenotonsillar hypertrophy in children, adenotonsillar hypertrophy is not likely the sole cause of sleep-disordered breathing in this age group. Rather, large tonsils and adenoids appear to precipitate OSAS in children with underlying abnormalities of upper airway function. Normal children have a relatively narrow upper airway, but maintain airway patency during sleep because of increased upper airway neuromotor tone and an increased central ventilatory drive. We speculate that OSAS occurs in those children lacking the compensatory upper airway neuromotor responses.