This study utilized computerized tomography (CT) to evaluate the effects of uvulopalatopharyngoplasty (UPPP) on upper airway (UA) dimensions. The objectives were to determine whether CT scan results would be useful in identifying UA characteristics predictive of a good surgical result as well as elucidating reasons for failure of this operative procedure. Twenty-three male patients with obstructive sleep apnea (OSA) had CT scans and polysomnography performed before and after UPPP. Preoperatively, the apnea plus hypopnea index (AHI) was 64 +/- 6 per hour and the minimal UA cross-sectional area (Amin) was located at 10 and 20 mm below the level of the hard palate in 87% (20 of 23) of the patients. Uvulopalatopharyngoplasty more than doubled UA cross-sectional areas at these two proximal levels. In contrast, the hypopharyngeal segment located 50 to 70 mm below the hard palate decreased in cross-sectional area by 23 to 25% after surgery. Eight patients (35%) had a good response to UPPP based on a greater than 50% decrease in AHI. Preoperatively, seven of these eight patients had Amin located 20 mm below the hard palate. Uvulopalatopharyngoplasty increased Amin and oropharyngeal cross-sectional areas to a greater extent in the good than in the poor responders. A poor response to UPPP was associated with preoperative Amin greater than 1 cm2, location at site other than 20 mm below the hard palate, and postoperative narrowing at the level of the hard palate. Patients with Amin less than 1.0 cm2 located 20 mm below the hard palate (lower velopharynx) were most likely to obtain a favorable result with surgery.