The purpose of this study was to pursue the morphology and position of mandibular symphysis and the positionion of lower incisors in 36 male and female adults with severe skeletal Class III malocclusion indicated for surgrcal orthodontic treatment. The following results were obtained. 1. Skeletal Class III malocclusion samples had thinner lavbio-lingual depth and more lingual inclination of mandibular symphysis than that of normal occlusion in both sexes. 2. Male and female with the skeletal Class III malocclusion showed marked lingual tipping of lower incisors. 3. In skeletal Class III malocclusion samples, lingual basal bone was thinner than that of normal occlusion in both sexes.