The success of uvulopalatopharyngoplasty in treating obstructive sleep apnea varies considerably. Some of this variability may be accounted for by differences in the site of upper airway narrowing. To determine whether preoperative awake upper airway and soft tissue volumes predict the response to uvulopalatopharyngoplasty, preoperative awake computed tomograms (CT) of the upper airway were performed on 60 consecutive patients with symptomatic obstructive sleep apnea. Tracings were made from the CT scans of upper airway, tongue, and soft palate. Computer software was used to determine the cross-sectional area and volume of the upper airway, tongue, and soft palate. Patients underwent overnight polysomnograms before and 3 months after uvulopalatopharyngoplasty. Tongue volume was larger (p less than 0.02) and both upper airway to tongue volume (p less than 0.0005) and oropharynx to soft palate volume ratios (p less than 0.01) were smaller in obese patients. A good response to uvulopalatopharyngoplasty as defined by a postoperative apnea index of less than 5 apneas/h or a reduction in apnea index greater than or equal to 50% was seen in 50 patients (83%). Patients who had a good response had a smaller oropharyngeal cross-sectional area (p less than 0.01), a smaller upper airway volume (p less than 0.05), a smaller upper airway to tongue volume ratio (p less than 0.01), and a smaller oropharynx to soft palate volume ratio (p less than 0.05). Obese patients with obstructive sleep apnea have larger tongues and smaller upper airways relative to tongue and soft palate size. Patients with smaller upper airways, particularly relative to tongue and soft palate size, have a good response to uvulopalatopharyngoplasty.