Objectives <p>To evaluate the effectiveness and stability of a modified overlap method for manipulating proximal segments (PSs) during bilateral sagittal split osteotomy for correcting facial asymmetry and to identify risk factors contributing to Menton horizontal relapse.</p> Materials and Methods <p>This retrospective cohort study involved 62 consecutive adults with class III asymmetry who underwent bimaxillary surgery. Patients were classified in two groups according to surgical techniques: the overlap group (<i>n</i> = 31), in which the non-deviated PS was flared outward before aligning with the distal segment (DS), and the conventional group (<i>n</i> = 31), in which the PSs and DS were aligned in maximum contact. Computed tomographic scans were taken before surgery (T0), postoperative 1&#xa0;week (T1) and 1&#xa0;year (T2). Transverse ramus measurements and maxillo-mandibular segments movements were intergrouply compared. Correlations of Menton horizontal relapse with preoperative and intraoperative factors were also assessed.</p> Results <p>From T1-T0, the overlap group showed greater reductions in discrepancies for gonial width (4.09 ± 3.49 mm) and coronal ramus angle (3.67° ± 3.44°) compared to the conventional group (1.76 ± 2.55 mm; 1.70° ± 3.16°) (p = 0.004, 0.023). From T2-T1, relapses in both groups were ≤ 2 mm and ≤ 2°. No correlation was found between surgical techniques and Menton horizontal relapse.</p> Conclusions <p>The overlap method demonstrates effectiveness in correcting facial asymmetry, resulting in greater reductions in ramus discrepancies while maintaining mandibular stability one year postoperatively.</p> <p>Clinical Relevance.</p> <p>For severe facial asymmetry, clinicians may consider using the overlap technique to enhance postoperative facial appearance.</p>