This study proposes a system for classifying facial asymmetry with accompanying mandibular prognathism to facilitate choice of surgical method. We examined hard and soft tissue measurements obtained from posterior–anterior cephalometric radiographs and clinical facial photographs of 153 patients (86 male, 67 female), classifying them according to menton deviation with transverse asymmetry (T), maxillary cant (M), and lip cant (L). The T-group is subclassified according to direction of transverse asymmetry (H). Statistical analysis of menton deviation, cant and transverse asymmetry was performed for each group. The various relationships observed among the groups indicate that most cases (85%) were not effectively correctable using conventional surgical methods. As such, the authors believe that analysing facial asymmetry in terms of the classification system presented in this study and employing surgical methods appropriate to each case will help achieve more harmonious aesthetic outcomes.