The aim of this report is to describe a case presenting with complaints of orbital pain, altered facial sensation, nasal obstruction and unilateral spontaneous nose bleeding. Panoramic radiography and computerized tomography disclosed a large pedunculated heterogeneous mineral opacity with two impacted molar teeth invading the maxillary sinus. The patient was operated on under general anaesthesia. Microscopic examination of the surgical specimen revealed relatively dense, compact bone with sparse marrow tissue that was diagnosed as osteoma. Clinical characteristics and biological behaviour of this lesion were evaluated with special regard to the reliability of imaging modalities and surgical procedures.