OBJECTIVE This study examined the long-term skeletal stability of relatively large maxillomandibular advancement surgery in the treatment of obstructive sleep apnea syndrome (OSAS). METHODS The presurgical, immediate (< 1 month), and long-term (> 12 months) postsurgical cephalometric radiographs of 19 patients undergoing maxillomandibular advancement with simultaneous genioplasty for OSAS were studied. The cephalometric measurements and calculations were performed using a commercial cephalometric software. RESULTS Maxillary and mandibular advancement seems to be stable in the horizontal and vertical planes over the long term. There was no significant correlation between the amount of surgical advancement and the amount of postsurgical instability, with the exception of gonion in the vertical plane. CONCLUSIONS The results from this study indicate that large surgical advancements in OSAS patients result in relatively stable repositioning of the maxilla and mandible over the long term.