Osteomas of the paranasal sinuses rarely lead to intracranial manifestations. The authors report an unusual case of a frontal sinus osteoma leading to subdural emyema formation. A 19-year-old man presented with headache and fever one month after minor facial trauma. Neuroradiological studies revealed subdural empyema in left frontal lobe with moderate cerebral edema and a osteoma in the left frontal sinus with sinusitis of maxillary sinus. The patient was surgically treated in one stage operation of decompressive craniectomy, removal of subdural empyema with frontal sinus osteoma, and endoscopic sinus surgery via cranial and nasal route. The patient recovered very well after surgery and postoperative antibiotic therapy. The etiology of intracranial infection and the treatment strategy are to be discussed.