This study assessed the relationship between temporomandibular disorders (TMD) and malocclusion in a group of 102 patients with horizontal mandibular deficiency who had elected mandibular advancement surgery. The prevalence of TMD as reflected by the overall Craniomandibular Index, Dysfunction index, and Muscle index scores was within the range of non TMD populations (mean Craniomandibular Index = 0.14; mean Dysfunction index = 0.12; mean Muscle index = 0.15). Forty-two percent of the patients exhibited essentially no signs of TMD, 7.8% had primarily muscle tenderness to palpation, 36.3% had joint sounds with or without temporomandibular joint tenderness, and 13.7% had combined muscle-joint signs. There were no convincing correlations among any of the cephalometric variables and Craniomandibular Index, Dysfunction index, and Muscle index scores. A subgroup of 30 of this patient population was evaluated both before and during orthodontic treatment just prior to surgery. No statistically significant changes were found in Craniomandibular Index, Dysfunction index, or Muscle index scores. Thus, a period of orthodontic treatment in these patients does not appear to increase the probability of TMD. e r o c s .