Osteomas are benign osteoblastic tumors that occur mainly in the fronto-ethmoid areas ofthe head and neck region. When they occasionally occur in the temporal bone, the external auditory canal is the most common site of origin; they rarely occur in the mastoid region. Moreover, mastoid osteoma with mastoiditis is an extremely rare entity in the temporal bone. Recently, the authors experienced a case of mastoid osteoma with mastoiditis in the left temporal bone. The mastoid osteoma was completely resected itself without a mastoidectomy, only for correction of the cosmetic deformity; the mastoiditis was not treated. Hence, the authors report the first case of a mastoid osteoma with mastoiditis in Korea, along with a review of the related literature.