The purpose of this study was to investigate the positional changes of the mandibular condyles after orthognathic surgery in patients with severe skeletal Class III malocclusion. This study was based on 21 patients who had received bilateral sagittal split osteotomy for mandibular setback. Among them 14 were fixated non-rigidly (W group), and 7 were fixated rigidly (R group). After submental vertex view analysis each subject was given the T.M.J. Tomogram in both centric occlusion and centric relation immediate before, 4~6 weeks after and more than 6 months after surgery. The anteroposterior and vertical changes between each time interval were measured and analyzed statistically. Fallowing results were obtained. 1. There was no significant difference between right and left condyles in their anteroposterior and vertical changes of the condylar position. 2. In anteroposterior changes of condylar positon of the wire fixation group, the condyles were moved anteriorly 4-6 weeks after surgery, and then the pattern of reestablishment to their preoperative position was observed more than 6 months after surgery. In the rigid fixation group, there was no significant difference in any observation periods of centric occlusion and centric relation. 3. In vertical changes of condylar position of the wire fixation group, the condyles were moved inferiorly 4-6 weeks after surgery, and then the pattern of reestablishment to their preoperative position was observed more than 6 months after surgery. In the rigid fixation group, the condyles were moved inferiorly 4-6 weeks after surgery, and then the pattern of reestablishment to their preoperative position was observed more than 6 months after surgery in centric occlusion only.