To obtain the best results in the treatment of patients with Angle Class III malocclusion, the etiologies of the malocclusion should first be clarified, and then an appropriate treatment modality should be decided. Angle Class III malocclusions in 120 subjects who had orthognathic surgery were analyzed with cephalometrics and facial photos and classified into 3 categories based on the abnormalities of the maxilla. Type A is true mandibular prognathism, which means that the maxilla is normal but the mandible is overgrown. Type B is characteristic of the overgrown maxilla and mandible with anterior crossbite. Type C indicates a hypoplastic maxilla with anterior crossbite. Treatment modalities should be differentially decided according to this new classification of Angle Class III malocclusions. (Int J Adult Orthod Orthognath Surg 2001;16:19–29)