There is evidence that narrowing or collapse of the pharynx contributes to obstructive sleep disordered breathing (SDB) in adults and children. However, studies in children have focused on those with relatively severe SDB who generally were recruited from sleep clinics. Thus, it is unclear whether children with mild SDB who primarily have hypopneas, and not frank apnea also have more collapsible airways. We estimated airway collapsibility in ten control subjects (9.4 ± 0.5 years old; 1.9 ± 0.2 hypopneas per hour) and seven children with mild SDB (10.6 ± 0.5 years old; 11.5 ± 0.1 hypopneas per hour) during stable, NREM sleep. None of the subjects had clinically significant enlargement of the tonsils or adenoids, nor did they undergo previous tonsillectomy or adenoidectomy. Airway collapsibility was measured by brief (2 breaths duration) and sudden reductions in pharyngeal pressure by connecting the breathing mask to a negative pressure source. Negative pressure applications, ranging from -1 to -20 cmH₂O, were randomly applied in each subject while respiratory airflow and mask pressure were measured. Flow-pressure curves were constructed for each subject, and the x-intercept gave the pressure at zero flow, the so-called critical pressure of the upper airway (Pcrit). Pcrit was significantly higher in children with SDB than in controls (-10.8 ± 2.8 vs. -15.7 ± 1.2 cmH₂O, P < 0.05). There were no significant differences in the slopes of the pressure-flow relations, nor in baseline airflow resistance. These data support the concept that intrinsic pharyngeal collapsibility contributes to mild SDB in children.