Because it has been suggested that patients with obstructive sleep apnea have a narrower pharyngeal airway than normal persons, we performed lateral fluoroscopy and computed tomographic (CT) scans of the pharynx in patients with this syndrome. Fluoroscopy in 6 sleeping patients showed that the obstruction always began during inspiration when the soft palate touched the tongue and posterior pharyngeal wall. The CT scans in 9 awake subjects demonstrated that the narrowest section of the airway in patients and in control subjects was the region posterior to the soft palate. The cross-sectional area of this region was significantly narrower in patients than it was in control subjects (p less than 0.001). Because a narrow airway would be more likely to collapse during inspiration than a normal one would (Bernoulli's Principle), we conclude that the narrow airways we observed in awake patients may be an important contributing factor in the pathogenesis of obstructive sleep apnea.