OBJECTIVE : The study purpose was to assess whether mandibular setback surgery by intraoral vertical ramus osteotomy (IVRO) induces obstructive apnea and hypopnea in healthy Class III patients without a history of respiratory dysfunction. We hypothesized that the apnea-hypopnea index (AHI) would not exceed 5 events per hour after surgery. METHODS : A prospective cohort study was conducted. The sample was composed of healthy Class III patients without a history of obstructive sleep apnea treated with isolated mandibular setback surgery by the IVRO procedure at a university hospital. In-home respiratory sleep recordings (Nox T3; Nox Medical, Reykjavik, Iceland) and self-administered questionnaires were obtained before and at least 3 months after surgery. The AHI was the primary outcome variable. Other study variables were as follows: peripheral capillary oxygen saturation, oxygen desaturation index, snore index, body mass index, Epworth Sleepiness Scale, and Oral Impact on Daily Performance index. Descriptive and bivariate statistics were computed, and the significance level was set at .05. RESULTS : The sample was composed of 8 patients. The mean age at surgery was 23.2 years (range, 18.2 to 33.4 years). The mean amount of surgical setback was 4.3 mm (range, 2.5 to 7.4 mm). The mean body mass index was 24.2 kg/m2 (standard error [SE], 1.3 kg/m2) and 23.9 kg/m2 (SE, 1.4 kg/m2) at the presurgical and postsurgical sleep recordings, respectively. The mean AHI was 1.3 events per hour (SE, 0.3; range, 0.1 to 2.5) before surgery and 1.8 events per hour (SE, 0.4; range, 0.3 to 3.3) after surgery. No statistically significant changes in AHI (P = .412), peripheral capillary oxygen saturation (P = .443), oxygen desaturation index (P = .194), snore index (P = .363), or Epworth Sleepiness Scale (P = .812) were observed. The patients' self-reported oral health-related quality of life was statistically significantly improved after surgery (P = .034). CONCLUSIONS : Mandibular setback surgery with the IVRO procedure in the range of 2.5 to 7.4 mm did not induce obstructive sleep apnea, measured as an AHI above 5 events per hour, in the 8 healthy, young adult Class III patients presented in this study. More studies including larger patient samples are needed.