We report a case of osteoma with a dentigerous cyst occurring in the maxillary sinus of a 24-year-old woman. The patient was referred to our hospital because of a radiopaque lesion in the left maxillary sinus. Computed tomographic examination revealed a high density radiopaque lesion containing a cystic lesion. The mass, measuring 16.5 × 14.0 × 18.5mm, and the cyst were removed surgically via the canine fossa with the patient under general anesthesia. The histopathological diagnosis was osteoma spongiosum with a dentigerous cyst. This case is very rare with respect to the structure and location of the lesion.
