BACKGROUND It has long been claimed that presurgical orthodontics is crucial to the outcome of surgical-orthodontic treatment for dentofacial deformity. However, in the literature, the effect of presurgical orthodontics on the treatment outcome remains controversial. The purpose of the study was therefore to investigate the effect of presurgical orthodontics on the treatment outcome in terms of facial aesthetics, occlusion, stability, and efficiency. METHODS Thirty-three adult patients with skeletal class III open bite corrected by Le Fort I posterior impaction and bilateral sagittal split osteotomy were included. The patients were divided into two groups: 13 received presurgical orthodontics, and 20 did not. Cephalometric radiographs and study models were used to evaluate the treatment outcome. RESULTS There were no between-group differences in facial aesthetics, overbite, or Peer Assessment Rating score. Overjet was larger in the no-presurgical orthodontics group than in the presurgical orthodontics group, but both were within normal limits. Both groups had similar maxillary and horizontal mandibular stability. Although the vertical mandibular stability was worse in the no-presurgical orthodontics group than in the presurgical orthodontics group, the direction of instability was favorable for open bite correction. Finally, longer treatment time was required in the presurgical orthodontics group compared with the no-presurgical orthodontics group (512±103 days versus 342±127 days; p<0.001). CONCLUSIONS The results suggest that in surgical-orthodontic correction of skeletal class III open bite, presurgical orthodontics has no clinically significant effects on facial aesthetics, occlusion, or stability. However, presurgical orthodontics has a significant adverse effect on efficiency. Patients receiving presurgical orthodontics undergo longer treatment time than those receiving no presurgical orthodontics.