Objective To assess the 6-month efficacy of uvulopalatopharyngoplasty (UPPP) compared with expectancy in selected patients with obstructive sleep apnoea syndrome (OSAS).

Design A prospective single-centre randomised controlled trial with two parallel arms stratified by Friedman stage and body mass index (BMI).

Participants 65 consecutive patients with moderate to severe OSAS (apnoea-hypopnoea index (AHI) ≥15 events/h sleep), BMI <36 kg/m², Epworth sleepiness scale ≥8, Friedman stage I or II.

Intervention Surgical treatment with UPPP. The control group underwent UPPP after a delay of 6 months.

Outcomes Changes in AHI and other polysomnography parameters at baseline compared with the 6-month follow-up.

Results All patients (32 in the intervention group and 33 in the control group) completed the trial. The mean (SD) AHI in the intervention group decreased significantly (p<0.001) by 60% from 53.3 (19.7) events/h to 21.1 (16.7) events/h . In the control group the mean AHI decreased by 11% from 52.6 (21.7) events/h to 46.8 (22.8) events/h, with a significant difference between the groups (p<0.001). The mean time in the supine position and the BMI were unchanged in both groups. Subgroup analyses for Friedman stage, BMI group and tonsil size all showed significant reductions in AHI in the intervention group compared with controls. There were no severe complications after surgery.

Conclusions This trial demonstrates the efficacy of UPPP in treating selected patients with OSAS with a mean reduction in AHI of 60% compared with 11% in controls, a highly significant and clinically relevant difference between the groups.

Trial registration number NCT01659671.