A patient with nasopharyngeal carcinoma (NPC) treated by radiotherapy developed tension pneumocephalus due to a naso-cranial fistula. The fistula was due to a pathological fracture at the base of skull affected by bone necrosis. The clinical features, neuro-radiological and post-mortem findings are presented. This is the first case report of pneumocephalus in association with NPC. The brain showed florid subarachnoid and intraventricular air collection under tension, low grade meningitis, foreign body giant cell reaction in the arachnoid membrane and multifocal cerebral infarction. Late radiation necrosis was also found in the left temporal lobe. The cause of the tension pneumocephalus in relation to radiation bone necrosis and the possible role of pneumocephalus in producing the multifocal cerebral infarction are discussed. The more common radiation necrosis of brain is also discussed. The pathogenesis of the pneumocephalus in this patient is distinctly different from the more common causes such as head injury and surgery.