Osteoma is the most common benign tumor of the nose and paranasal sinuses, and the frontal sinus osteomas were asymptomatic, and were discovered only when developing compression symptroms and other complications of a space-occupying lesion. A patient with proptosis was referred from Ophthalmology Department, radiological examination revealed a huge bony density lesion occupying the whole left frontal sinus with ethmoid sinus, orbit and intracranial extension. The patient was managed with osteoplasty operation and dura reconstruction with pericranial flap in April 1993. There is a good cosmetic result. No recurrence or other complications have been noted after follow-up for one year postoperatively.