To assess the effect of uvulopalatopharyngoplasty (UPPP) on positional dependency in patients with obstructive sleep apnea (OSA).Retrospective analysis.Tertiary care university hospital.Ninety-six patients who underwent UPPP because of OSA from June 1, 2004, through July 31, 2008, were included. Both preoperative and postoperative attended full-night polysomnography were conducted in all patients. Positional dependency was diagnosed if the patient's apnea-hypopnea index score in the supine position was more than twice as high as that in the lateral position.Position-specific outcomes of UPPP, such as the success rates in the supine or lateral position, were assessed, as well as overall treatment outcomes. The outcomes were also analyzed according to the severity level of the apnea-hypopnea index in each position. The change of positional dependency after UPPP was evaluated.The apnea-hypopnea index score in the lateral position was markedly reduced after UPPP in position-independent patients (P = .02). However, the overall success rates were only 31.8% and 34.6% in patients with and without positional dependency, respectively. The success rate in the lateral position was 68.2% in position-independent patients and 32.7% in position-dependent patients (P = .01). In addition, 14 of 22 patients with position-independent OSA (64%) gained positional dependency after UPPP.Uvulopalatopharyngoplasty is successful treatment for obstructive events occurring in the lateral sleep position, especially in patients without positional dependency. This implies that patients who have become position dependent may benefit from positional therapy after UPPP.