A 46-year-old man presented with severe tension pneumocephalus triggered by mild head injury 7 years after craniotomy. He had a history of subarachnoid hemorrhage due to ruptured anterior communicating artery aneurysm, coating of the aneurysm performed via a craniotomy, and a ventriculoperitoneal (VP) shunt inserted. He fell from bed in a rehabilitation hospital. Eight hours after the injury, he became comatose and suffered general convulsion. He was then transferred to our hospital. Radiography and computed tomography (CT) revealed a large amount of intracranial air and a widely opened frontal sinus. On the day of admission, the shunt tube was ligated. Surgery was performed to repair the dura mater and close the frontal sinus. Postoperative CT revealed reduction in the amount of air and frontal sinus obstruction. The patient had a good postoperative course without meningitis. Tension pneumocephalus may occur as a complication several years after a craniotomy because of the chronic lowering of intracranial pressure induced by a VP shunt. Complete frontal sinus repair is important during the initial craniotomy.