We prospectively compared the efficacy of anterior palatoplasty and the uvulopalatal flap procedure for the treatment of patients with mild and moderate obstructive sleep apnea syndrome (OSAS). Our study group was made up of 45 patients who had been randomly assigned to undergo one of the two procedures. Palatoplasty was performed on 22 patients-12 men and 10 women, aged 28 to 49 years (mean: 39.2)-and the flap procedure was performed on 23 patients-14 men and 9 women, aged 28 to 56 years (mean: 41.3). Our primary outcomes measure was the difference in pre- and postoperative apnea-hypopnea index (AHI) as determined by polysomnography at 6 months after surgery. Surgical success was observed in 18 of the 22 palatoplasty patients (81.8%) and in 19 of the 23 flap patients (82.6%). Compared with the preoperative values, mean AHIs declined from 17.5 to 8.1 in the former group and from 18.5 to 8.6 in the latter; the improvement in both groups was statistically significant (p < 0.001). In addition, significant postoperative improvements in both groups were seen in mean visual analog scale (VAS) scores for snoring, in Pittsburgh Sleep Quality Index values, and in Epworth Sleepiness Scale scores (p < 0.001 for all). VAS scores for pain at rest were significantly lower in the palatoplasty group than in the flap group at 2, 4, and 8 hours post-operatively and on postoperative days 4 through 7 (p < 0.002). Likewise, VAS scores for pain during swallowing were significantly lower in the palatoplasty group at 2, 4, 8, and 16 hours and on days 4 through 7 (p < 0.009). We conclude that both anterior palatoplasty and uvulopalatal flap procedures are effective for the treatment of mild and moderate OSAS in patients with retropalatal obstruction. However, our comparison of postoperative pain scores revealed that anterior palatoplasty was associated with significantly less morbidity.