Objectives: Assessment of the long-term effect of uvulopalatopharyngoplasty (UPPP) on snoring, excessive daytime sleepiness, and nocturnal oxygen desaturation index (ODI) in patients with obstructive sleep apnea syndrome. Study Design: Evaluation of snoring, excessive daytime sleepiness, and ODI in patients treated by UPPP earlier. Materials and Methods: Patients (n ؍ 58) with a follow-up period of 11 to 74 months (median, 34 mo) were included in this study. Snoring and excessive daytime sleepiness were scored on specially designed semiquantitative scales. In all patients ODI was calculated from pulseoximetry combined with polysomnography at base line and by polygraphy (MESAM 4) during follow-up in 38 patients. Long-term response was compared with 6-month response in the same cohort. Results: There was a long-term improvement of snoring in 63% of patients, no change in 23%, and a deterioration in 14% (P < .00001). Overall snoring increased slightly between 6 months and long-term follow-up. There was an improvement of excessive daytime sleepiness in 38%, no change in 27%, and a deterioration in 35% (P ؍ .80). Excessive daytime sleepiness showed a relapse to preoperative levels between 6 months and long-term follow-up. The median improvement of ODI was ؊1 (95% interpercentile range, 73-51) and was not significant (P ؍ .35). In 5 of 13 patients in whom ODI at baseline exceeded 20, ODI was reduced to less than 20. In 4 of the 38 patients ODI was reduced to less than 5. The improvement of ODI decreased significantly between 6 months and long-term follow-up (P ؍ .03). No relation was found between body mass index, Mueller maneuver, X-cephalometry, and long-term outcome. An additional finding was that the ODI decreased after UPPP in combination with tonsillectomy, compared with a slight increase after UPPP alone; the difference was significant (P ؍ .008). Conclusion: The response to UPPP for obstructive sleep apnea syndrome decreases progressively over the years after surgery. UPPP in combination with tonsillectomy was more effective than UPPP alone.