The mandibular symphysis is preferred as a donor site for the relatively small grafts needed for the autogeneous bone graft procedure. This study was undertaken to determine the morphology and composition of the cortical and trabecular bone in the mandibular symphyseal region using 35 mandible specimens from Koreans. The topographical patterns through the thickness of the cortical plate and the width of the trabecular bone were observed. In this study, the labial cortical plate of the mandible became thicker from the superior to the inferior aspects (P < 0.05). However, the trabecular bone width exhibited a different distribution pattern compared to the thickness of the labial cortical plate. This observation concerning the cortical and trabecular bones assists in determination of the depth of osteotomy. The results provide useful information on the mandibular symphysis graft prior to dental implant placement. These results will enable the volume of the cortical plate in the mandibular symphyseal region and its proper size, depth, and location to be predicted when removing a graft block.