Skeletal asymmetry in patients who undergo orthognathic surgery is frequently associated with postoperative temporomandibular joint (TMJ) disorders caused by condylar rotation. This study was designed to elucidate the relation between changes in the condylar long axis and TMJ function after bisagittal split osteotomy (BSSO). A total of 42 patients with mandibular prognathism underwent BSSO. Split osseous fragments were secured by standard titanium plates in 22 patients bent titanium plates were used to secure fragments in 20 patients. The angle of the bent plates was adjusted to avoid displacement of the condyle after osteotomy, as compared with condylar position on preoperative submental-vertical (S-V) cephalograms. The postoperative position or the condyle was assessed on X-ray film, and changes in TMJ function were evaluated. The condylar long axis differed significantly on X-ray film between patients using a standard titanium plate and those using a bent plate (P<0.05). and no sign of TMJ functional impairment was noted in the bent-plate group. Although the use of bent plates requires further study, maintenance of a suitable position of the condyle relative to the condylar axis is one of the conditions for a successful outcome of BSSO.