Bilateral third nerve palsy often points to the involvement of its nucleus. Third nerve palsy as a result of posttraumatic nuclear involvement is an extremely rare condition. A 23-year-old man presented with a depressed skull fracture after acute head trauma and had Glasgow Coma Scale Score of 9. The diameters of the pupils were 6.5 and 7.5 mm and they were not reactive to light stimulation. There was bilateral ptosis. Computed tomography (CT) relieved bilateral perimesensephalic pneumocephalus. We suggested that bilateral oculomotor nerve paresis might develop in association with posttraumatic bilateral perimesensephalic pneumocephalus, which affected the nucleus of the third nerve.