Paranasal sinus osteomas are benign slow growing tumors, occasionally known to cause complications for a long time. Frontobasal extension of paranasal sinus osteoma is an uncommon localization. We present a 20 year-old-man admitted to our clinic with a complaint of pus drainage and wound from forehead for 2 weeks. The radiological images of the patient revealed a mass mimicking osteoma and extending into the frontal sinus and frontobasal area with a chronic infection. The patient was initiated antibiotics for 2 weeks and the mass was extirped through the destructed anterior wall of frontal sinus. The histopathological diagnosis was osteoma and the patient was discharged uneventfully at the 7th day after the operation.