Children snore less than adults, and have fewer obstructive apneas, suggesting a less collapsible upper airway. We therefore hypothesized that the compensatory upper airway responses to subatmospheric pressure loading decrease with age, due to changes in upper airway structure and ventilatory drive. We measured upper airway upstream-pressure/flow relationships during sleep in 20 non-snoring, non-obese children and adults. Measurements were made by correlating maximal inspiratory airflow with the level of nasal pressure applied via a mask. The slope of the upstream-pressure/flow curve (SPF) was used to characterize upper airway function. We found that children had a flatter slope than adults (8 + 5 vs 30 + 18 ml/s/cm H2O, P < 0.002), and that SPF correlated with age (r = 0.62, P < 0.01) and body mass index (r = 0.62, P < 0.01). The occlusion pressure in 100 milliseconds (P0.1) during sleep was measured in 6 children and 2 adults; it correlated inversely with SPF (r = -0.80, N = 8; P < 0.02). We conclude that the upper airway compensatory responses to subatmospheric pressure loading decrease with age. This is associated with increased body mass index, even in non-snoring, non-obese subjects. Ventilatory drive during sleep plays a role in modulating upper airway responses. Further studies will evaluate the developmental response of hypercapnia on upper airway reflexes.