Objective: To evaluate the long-term effects of mandibular symphyseal distraction osteogenesis (MSDO) on the correction of class II malocclusion correction and dental crowding. Materials and Methods: Twenty-two patients received MSDO and presented class II malocclusion with transverse mandibular discrepancy. The authors collected data on 2 different cephalometric analyses. On Tweed analysis, The authors recorded ANB, SNA, SNB, and FMA angles. On Delaire analysis, we recorded the distance from Pti (pterygoid inferior) to ENAt (anterior nasal spine) and the distance from Cos (superior condyle) to Pog (pogonion). Superimpositions studies were performed at pre-treatment phase (T1) and post-treatment phase (T2) to evaluate the new position and changes in the dimensions of the mandible and maxilla. Results: On superimposition of Tweed analysis of T1 and T2, reduction of ANB was seen in 18 patients, no change in ANB in 2 patients, and increase in ANB (by 1 deg) in 2 patients. Superimposition of Delaire analysis showed a mean difference of 0.3 mm (SD, 3.6 mm) between T1 and T2 for the maxilla and a mean difference of 6.0 mm (SD, 7.3 mm) for the mandible. Conclusions: Mandibular symphyseal distraction osteogenesis performed after the pubertal growth peak can effectively correct class II malocclusion and dental crowding with a single light surgical procedure.