Large osteomas of the fronto-ethmoidal cavities are very rare benign tumors. Headache and ocular signs are the most common symptoms. Imaging allows the diagnosis. Treatment of ethmoid sinus osteoma is surgical. One case with orbital extension is reported and discussed. A 30 years-old male; complaining of swelling of themedial angle of the right eye. Computed tomography showed a right ethmoidal process with orbital extension. The tumor was removed through an external ethmoidectomy.