A prominent role for upper airway neuromuscular control mechanisms in the pathophysiology of pediatric obstructive sleep apnea syndrome (OSAS) is suggested by the observation that obstruction does not occur during wakefulness and is infrequently seen during non-REM sleep. Using a custom intraoral surface electrode to record genioglossal activity (genioglossal electromyography [EMGgg]), normalized with a maximal maneuver, we studied 10 children with OSAS and 6 normal control subjects to determine EMGgg activity during (1) wakefulness, (2) the sleep onset period, and (3) stable non-REM sleep. We observed that the EMGgg activity in patients with OSAS compared with control subjects was significantly greater during wakefulness (3.6 +/- 1.8 vs. 1.6 +/- 1.8% maximum, p < 0.05) and had a greater decline during the early and late sleep onset period (p < 0.05). During stable non-REM sleep, EMGgg remained below the wakeful baseline in all normal control subjects but increased above the baseline in four of the patients with OSAS. We speculate that the increased EMGgg activity during wakefulness represents a reflex-driven neuromuscular compensation for an anatomically compromised airway. Furthermore, the larger decline in EMGgg at sleep onset observed in patients with OSAS is consistent with the relative loss of this reflex. Finally, the return of EMGgg activity above baseline in patients with severe OSAS suggests that some chemical or mechanical compensatory mechanisms remain active during stable non-REM sleep in children.