Orbital osteoma is an uncommon tumor. We report a case of orbital osteoma originating from the ethmoidal bone in a 59-year-old female. She was referred to our hospital in 1992 because of progressive exophthalmos. A CT scan showed a high density mass at the ethmoidal bone extending into the right orbit. It was diagnosed as an orbital osteoma. 6 years later she experienced diplopia. Therefore, we decided to excise the tumor. The removed solid tumor measured 15×20×30mm, and the histological diagnosis was a compact type of osteoma. After surgery, all ophthalmic symptoms disappeared.