Ossifying fibroma is a rather uncommon fibro-osseous tumour which can involve the bones of the paranasal sinuses and produce proptosis. This tumour has generally been difficult to differentiate clinically and histopathologically from fibrous dysplasia and other fibro-osseous tumours of the paranasal sinuses. A case of ossifying fibroma in the maxillary sinus, seen in a 16-year-old male, was reported. The patient presented a painless and slowly enlarged mass on the left suborbital region. X-ray films revealed a large, well circumscribed hard mass shadow which filled in the left maxillary sinus. CT scans revealed the same finding and the anterior wall of the maxillary sinus was suspected as the origin of the tumor. Biopsy of this tumor showed fibrous dysplasia, but the histological examination on the surgically removed tumor was diagnosed as ossifying fibroma. Differential diagnosis, and clinical and histopathological features between ossifying fibroma and fibrous dysplasia are discussed.
