The purpose of this study was to aid in the evaluation of prognosis of temporomandibular joint following orthognathic surgery. For this study, 20 patients (40 TMJ) who undergone orthognathic surgery were examined. Preoperative and postoperative tomograms of TMJ were taken. And the subjects were divided into 3 groups according to postoperative periods. The obtained results were as follows; 1. There were no significant differences between preoperative and postoperative changes in joint spaces in each group and between groups(P<0.05). 2. There were no significant differences between preoperative and postoperative ratio of joint space(P<0.05). 3. There were no significant differences between preoperative and postoperative changes in the range of motion of condylar head(P<0.05). 4. The bony changes of condylar head were observed in 14(35%) condyles (6 erosion, 2 flattening, 5 double contour, 1 osteophyte).