Objectives: We evaluated the effects of uvulopalatopharyngoplasty (UPPP) on the work of breathing (WOB) in obstructive sleep apnea syndrome (OSAS). Methods: Fifteen healthy subjects and 30 subjects with OSAS who desired UPPP were prospectively enrolled. All underwent measurement of WOB while awake as well as in a sleep study. These studies were repeated 3 months after UPPP in the patients with OSAS. Results: In OSAS before UPPP, the WOB while supine was increased above that of normal subjects. After UPPP, the WOB while supine remained elevated in those whose OSAS did not respond to surgery, and it returned to normal levels in patients whose OSAS improved after UPPP. Conclusions: Abnormal WOB in patients with OSAS returns to normal if UPPP results in amelioration of OSAS.