To determine its predictive value, polysomnography was performed on 14 snorers with sleep apnea syndrome (SAS) before and 3 months after uvulopalatopharyngoplasty (UPPP). In the 8 patients considered as cured (less than 10 apneas per hour after UPPP), total apnea index (TAI) decreased from 29.7 +/- 22.6 to 4.9 +/- 3.5. Rapid eye movement sleep (REM) increased from 10.9 +/- 3.6 to 14 +/- 5.7% of the total sleep period (TSP). In the 6 uncured patients, TAI decreased from 59.7 +/- 15.7 to 32 +/- 15.7 and REM increased from 7.7 +/- 5.6 to 15.8 +/- 7.2% of TSP. Snoring and drowsiness decreased in both cured and uncured patients. A presurgical apnea index less than 40 seems to be a reliable predictor of successful UPPP. The association of obstructive apnea with either central apnea or mixed apnea was not a factor of poor prognosis. Better sleeping could explain in part the clinical improvement in both cured and uncured patients, but postoperative polysomnography is needed to detect asymptomatic SAS.