Osteoma of the paranasal sinus is relatively rare benign tumor, but is the most common one. It is frequently developed at young aged male. And its pathogenesis is still questionable, but several theory (1. traumatic, 2. inflammatory, 3. embryologic 4. etc.) was reported. Recently the authors had experienced one case of osteoma originated from right ethmoid sinus extended onto the frontal region, which was removed by external frontoethmoidectomy approach successfully. Postoperative condition was good and there was no evidence of recurrence during the about 8 months follow-up period.