Normal children have a smaller upper airway than adults, but, nevertheless, snore less and have less apnea. We have previously shown that normal children have an upper airway that is resistant to collapse during sleep. We hypothesized that this resistance to collapse is due to preservation of upper airway neuromotor responses during sleep. Furthermore, we hypothesized that upper airway responses would be diminished in children with the obstructive sleep apnea syndrome (OSAS). We therefore compared the upper airway pressure-flow relationship during sleep between children with OSAS and controls. Measurements were made by correlating maximal inspiratory airflow with the level of nasal pressure applied via a mask. Neuromotor upper airway activation was assessed by evaluating the upper airway response to 1) hypercapnia and 2) intermittent, acute negative pressure. We found that children with OSAS had no significant response to either hypercapnia or negative pressure during sleep, compared with the normal children. After treatment of OSAS by tonsillectomy and adenoidectomy, there was a trend for normalization of upper airway responses. We conclude that upper airway dynamic responses are decreased in children with OSAS but recover after treatment. We speculate that the pharyngeal airway neuromotor responses present in normal children are a compensatory response for a relatively narrow upper airway. Further, we speculate that this compensatory response is lacking in children with OSAS, most likely due to either habituation to chronic respiratory abnormalities during sleep or to mechanical damage to the upper airway.