While osteomas often occur in the orofacial area, it is relatively rare for one to occur in the temporomandibular joint area. Here, we report a patient who underwent multidisciplinary treatment including high condylectomy for peripheral osteoma arising in the left mandibular condyle. The patient was a 46-year-old woman with the chief complaint of facial asymmetry. Cephalometric analysis revealed skeletal anterior crossbite due to anterior deviation of the mandible, with chin deviation of 10 mm to the right. A computed tomography scan revealed bone hyperplasia in the mesiodistal and inner areas of the left mandibular condyle, which exhibited outward anterior displacement. Bone scintigraphy showed a circular area of strong radioisotope accumulation with indistinct boundaries, consistent with the lesion in the left mandibular condyle. The above findings led to a diagnosis of skeletal mandibular prognathism with facial asymmetry due to peripheral osteoma originating in the left mandibular condyle. After orthodontic treatment and surgical resection of the tumor and mandibular condyle, preservation and prosthetic treatment were undertaken. A well-balanced facial appearance and good occlusion were achieved.