Subperiosteal hematoma of the orbit is a rare but well-recognized entity, usually caused by trauma. Two cases of subperiosteal hematoma associated with sinusitis are presented. A 44-year-old woman experienced the sudden onset of proptosis, and decreased visual acuity. Computed tomographic scanning and magnetic resonance imaging revealed a frontoethmoidal mucocele and a biconvex mass in the upper part of the left orbit. The mucocele was drained during nasal endoscopic surgery and the subperiosteal hematoma was evacuated during superior orbitotomy. A 42-year-old man had a headache and proptosis. Computed tomographic scan revealed sinusitis and subperiosteal orbital hematoma of the left orbit. Subperiosteal orbital hematoma associated with sinusitis is extremely rare but should be suspected in a patient with acute onset of proptosis in whom computed tomographic scanning reveals paranasal sinusitis.