Uvulopalatopharyngoplasty (UPPP) is an effective treatment for some patients with obstructive sleep apnea syndrome (OSAS). A major difficulty has been to select those patients who will have a good response to UPPP. Fiberoptic nasopharyngoscopy with Müller Maneuver (FNMM) was applied in preoperative evaluation of patients with OSAS to identify those in whom greatest pharyngeal collapse was in the region of the tonsillar fossae and soft palate. Those with pharyngeal changes on FNMM who were considered most likely to respond to surgery underwent UPPP. Comparison of pre and postoperative polysomnography reveals significant (p less than .001) improvement in indices of severity of OSAS The mean apnea index (apneas per hour) was diminished by 72%. Eighty-seven percent of patients had greater than 50% reduction in apnea index. Preoperative selection of OSAS patients by FNMM increases the likelihood of success of UPPP.