Aim and Background: This retrospective study evaluated the changes in adenoid and pharyngeal airway spaces associated with surgical mandibular setback in skeletal Class III patients. Patients and Methods: Pre- and one- year-post-operative lateral cephalograms of 25 adult patients with mandibular prognathism who had bilateral sagittal split osteotomy (BSSO) were traced. Cephalometric parameters including SNA, SNB, GoGn to SN, y-axis, SPPS, MPS, IPS, PNS-Eb, at-atp, ppw-Ba were calculated, compared, and then data were analyzed using Paired t-test or Sign test. The role of growth pattern and gender factor was analyzed with Fisher exact test. MannWhitney test was utilized to compare between the groups of male/female as well as the groups of vertical/horizontal grower. The results were considered at a maximum level of significance of 5% (P < 0.05). Results: At long-term follow-up, 25 patients (m:8, f:17) with the mean age of 25±4; there was a decrease in MPS value (3.8±6.7) that statistically significant (P=0.001). Although an increase was found in PNS-Eb index (3.1±4.4), the changes were not significant (P=0.03). No significant change was observed in other parameters. Also, growth pattern and gender didn’t affect the mentioned parameters. Conclusion: Mandibular setback surgery causes a long-term effect in some parameters of pharyngeal airway space area. In patients suffering from obstructive sleep apnea or in case of some other risk factors including overweight, short necks, and small pharyngeal airway space, a mandibular setback surgery could possibly predispose to the development of sleep apnea syndrome.