Since the development of mandibular contouring surgery, there have been many unfavorable results due to technical reasons. Those results include asymmetry, undercorrection, overcorrection, and an incorrect contour line. Over three years the authors have analyzed 19 cases of unfavorable results and found the following: (1) There have been 7 cases of undercorrection, 5 cases of asymmetry, 5 cases of incorrect contour line, and 2 cases of overcorrection. (2) The main technical errors that cause unfavorable results seem to be the simple straight cutting of mandible angles instead of curved cutting using multistaged curved ostectomy. (3) We suggest that the basic way to prevent unfavorable results in mandibular contouring surgery is to contour the mandible, including angle, body, and symphysis, as a whole by way of multistaged curved ostectomy.