A new surgical procedure to treat obstructive sleep apnea by uvulopalatopharyngoplasty (UPPP) was evaluated in 66 patients, 63 men and 3 women, with objectively documented sleep apnea syndrome. Removal of redundant tissue in the oropharynx (UPPP) significantly improved excessive daytime sleepiness, reduced by half the frequency of apneas and hypoxia occurring during sleep, and improved the quality of sleep. Closer analysis indicated that all 66 patients did not benefit to the same degree. Among patients classified as responders, the frequency of apnea was reduced to a level seen in healthy adults of the same age, measures of sleep approached normal, and excessive daytime sleepiness was eliminated. In nonresponders, frequency of apnea and consequent disruption of sleep was not reduced, but nocturnal hypoxia was improved.