Although uvulopalatopharyngoplasty relieves obstructive sleep apnea in the majority of patients, the factors that determine a successful response are not well defined. To determine whether preoperative awake upper airway measurements predict the response to uvulopalatopharyngoplasty, presurgical lateral cephalometric radiographs were evaluated on 60 consecutive patients with symptomatic obstructive sleep apnea. Patients underwent overnight polysomnograms before uvulopalatopharyngoplasty and 3 months afterwards. Forty-eight (80%) patients had a good response as defined by a postoperative apnea index of less than or equal to 4 apneas/hour or a reduction in apnea index of greater than or equal to 60%. Responders had a significantly narrower inferior airway space (P less than .0005) and a smaller ratio of inferior airway space to tongue length (P less than .001). Improvement in apnea severity following uvulopalatopharyngoplasty was related to the degree of airway narrowing (r = 0.36; P less than .01). This study shows that upper airway measurements help predict response to uvulopalatopharyngoplasty in patients with obstructive sleep apnea. Patients with a narrow airway, particularly relative to tongue size, have good responses to uvulopalatopharyngoplasty.