The upper airway was evaluated in eight patients with obstructive sleep apnea by using a rapid sequential CT scanner (Imatron C-100). Four patients also had simultaneous polysomnograms to determine the onset of sleep and apnea. The upper airway was scanned while the patient was awake (eight patients), asleep (four patients), and asleep and apneic (eight patients). Measurements of the cross-sectional area of the upper airway were correlated with the findings on sleep studies in four patients. During the awake state the airway was narrowed and showed increased collapsibility in all eight patients. Five of the eight patients had cross-sectional areas of less than or equal to 4 mm2 at one or more sites at some time during the respiratory cycle while awake. During apnea all patients had obstruction at the uvula and oropharynx, but the length of the obstruction varied from one patient to another. In three of the eight patients the obstruction extended inferiorly to the hypopharynx. Cine CT can be used to objectively evaluate patients with sleep apnea and may demonstrate the need to modify surgical treatment.