This study utilized the kinesiograph to assess the effect of orthognathic surgery on mandibular rest positions in a group of 27 patients exhibiting vertical facial deformities (14 long faced and 13 short faced patients). Two distinct rest positions were confirmed--clinical and physiological. Following surgery to alter the vertical dimensions, the clinical freeway space was found to adapt immediately whereas the physiological rest position partially adapted in the immediate postoperative period and continued to do so over the following year.