Aims: This study was designed to determine the incidence of altered sensation in patients undergoing orthognathic surgery. Method: Seventy two patients who underwent orthognathic surgery between January, 1999 and December, 1999 constituted the study group. Seven patients were excluded because of lack of follow up. Sixty five patients were followed using objective and subjective neurologic testing during the period immediately following operation, 1 month, 2 months, 6 months, and 1 year postoperatively. Age ranged from 17 to 38 years, with a mean of 24.5 years. Male patients were 21, female 44. Twenty eight bilateral sagittal splitting ramus osteotomy(BSSRO) of mandible were performed, 35 BSSRO with genioplasty, 2 genioplasties. Information on the degree of intraoperative nerve encounter was obtained from the surgical reports in 47 patients and was divided into the following three categories: (1) the nerve was not encountered in 23 patients; (2) the nerve was exposed in 11 patients; (3) the nerve was exposed and repositioned from the proximal segment in 13 patients. Results: Four patients reported altered nerve sensation of lower lip and/or chin(6.2%) at final follow up. Two patients underwent BSSRO and the other two patients BSSRO with genioplasty. Three of the patients underwent nerve exposure during the operation. Conclusion: We suggest that the nerve exposure during the operation might be partly responsible for nerve dysfunction after orthognathic surgery.