In adults, the critical nasal pressure (Pcrit) at which the upper airway collapses is higher in patients with the obstructive sleep apnea syndrome (OSAS) than in those with primary snoring. Pediatric OSAS differs clinically from adult OSAS. We therefore compared Pcrit between prepubertal children with OSAS and primary snoring. Pcrit was determined by correlating the maximal inspiratory airflow with the level of positive or negative nasal pressure applied via a nasal mask. As in adults, we found that the maximal inspiratory airflow varied in proportion to the upstream (nasal) rather than the downstream (esophageal) pressure changes. Pcrit was 1 +/- 3 cmH2O in OSAS compared with -20 +/- 9 cmH2O in primary snorers (P < 0.002). In three OSAS patients reevaluated after tonsillectomy and adenoidectomy, Pcrit declined to -7.2 +/- 4.0 cmH2O. We conclude that the pediatric airway behaved as predicted by the Starling resistor model and that Pcrit, a measure of airway collapsibility, correlated with the degree of upper airway obstruction and was reduced postoperatively, consistent with increased upper airway stability.