Uvulopalatopharyngoplasty has been a standard surgical treatment of obstructive sleep apnea syndrome since its introduction. The effectiveness of the operation can be evaluated by improvement of symptoms and changes of variable parameters of polysomnography. We compared preoperative and postoperative symptoms of obstructive sleep apnea in 35 patients selected from those upon whom uvulopalatopharyngoplasty had been performed from March, 1988 to October, 1991. We also compared polysomnographic findings taken preoperatively and at the 8th week postoperatively. Postoperative complications were investigated. Twenty nine out of 35 patients(83%) showed improvement with a reduction of snoring. In relation to the symptoms of daytime somnolence and nocturnal restlessness, 24 out of 34 patients(71%) and 28 out of 35 patients(80%) showed improvement. Objective comparison of the postoperative status was achieved with the polysomnographic findings in 15 patients. Among the 15 patients, seven patients showed improvement in the apnea index below 60% of the preoperative level. Immediate postoperative complications within two weeks were dysphagia, nasal reflux, pain, hypernasality and the like. The late sequelae, six months after operation, were dry crust on soft palate, changes in taste sensation, and voice change. To find the predictive value of the apnea index and body mass index for alleviation of the symptoms, we classified the patients into two groups. One consisted of those who showed improvement in symptoms(responders) and the other was those who were in a stationary or rather aggravated state(nonresponders). The mean values of the two parameters were compared between the responders and nonresponders to the operation. Responders to the operation showed less preoperative apnea index and body mass index than the nonresponders. Although there was a significant difference between the objective and subjective results of the operation, uvulopalatopharyngoplasty is a recommendable surgical treatment modality with much benefit of improvement of the symptoms and with acceptable complications.