The purpose of this investigation was to study, by means of an electrognathographic procedure, mandibular motion after bilateral vertical ramus osteotomy for correction of mandibular prognathism in 27 adults. Each patient had kinesiographic registrations taken within 1 week before the operation and 6 months postsurgery. The results of the study demonstrated that, an average, orthognathic surgery did not adversely affect the postoperative mandibular motion. On the contrary, postoperative improvement in most of the varialbes was revealed by analysis of postoperative changes and comparison of the postoperative values with normative data.