We report a case of 14-year-old female who was admitted with a rare retroorbital subperiosteal hematoma manifested as sudden orbital pain, progressive proptosis and diminution of vision. Cranial computed tomography showed a biconvex high density mass in the superolateral part of the right orbit, which was recognized to be a subperiosteal hematoma intraoperatively. Infection extending into the orbit was important in causing the hemorrhage.