Steroid-induced osteonecrosis is a non-infectious and avascular bone-necrosis disease, which occurs in patients receiving steroids. The common site is the epiphysis of long trunk bones such as the femoral head; however, steroid-induced osteonecrosis rarely occurs in the stomatognathic system. We report a case of suspected steroid-induced osteonecrosis arising in the mandibular condyle. The patient was a 59-year-old woman, who visited a dental clinic because of right preauricular pain, swelling, and trismus. The symptoms disappeared and recurred repeatedly for 8 months. Therefore, she was referred to our hospital for further investigation. Moreover, she had undergone relatively long-term high dose steroid therapy for sudden deafness. Computed tomography revealed osteolytic changes around the right mandibular condyle. Magnetic resonance imaging revealed a lower intensity on T1-weighted images and a high intensity on T2-weighted images around the right mandible condyle area. Moreover, it showed swelling of right masseter muscle, inside and outside pterygoid muscles. Bone scintigraphy demonstrated abnormal diffuse accumulation of technetium-99m methylene diphosphonate (99mTc-MDP) in the region of the right mandible. On the basis of the imaging findings, osteomyelitis of mandible was diagnosed. We administered antibiotics and performed the following surgical treatment with the patient under general anesthesia: right mandibular segmentectomy and reconstruction with a free peroneal osteocutaneous flap. Histopathologic examination of the resected specimen revealed osteonecrosis of the mandible. There was no source of the odontogenic infection. Therefore, possible involvement of steroid-induced osteonecrosis in the development of these symptoms was assumed. The postoperative course was uneventful.