Three cases of tension pneumocephalus are reported and pathogenesis, clinical features and management of this complication is discussed. Case 1: A 12-year-old female underwent a craniotomy for a suprasellar tumor following V-P shunting. At that time, Mayfield's pin fixing head holder was used and a CSF leak from a puncture wound caused by the head holder was noted postoperatively. Although she showed uneventful recovery from the anesthesia, several hours after surgery, she developed general convulsions and deteriorated. CT scan revealed a huge bifrontal accumulation of air compressing the entire brain postero-caudally. No active measures were taken to treat the intracranial air and a follow-up CT scan revealed a hemorrhagic infarction in the right occipital lobe possibly caused by transtentorial herniation. The patient remained in a vegetative state until her death three years later. Case 2: A 55-year-old man had a pansinectomy for sinusitis. Seven days later he developed CSF rhinorrhea and a severe headache. A CT scan revealed air in the subarachnoid space as well as in the ventricles. After repeated spinal taps, he became stuporous. An emergency repair of the CSF leak was performed. Intraoperatively, the accumulation of air was noted in the subarachnoid space under extreme tension. He made a full recovery. Case 3: A 69-year-old woman underwent a neck clipping for a ruptured anterior communicating aneurysm 2 days after the onset. Shortly before the craniotomy, a continuous spinal drainage system was installed. Postoperatively she did not recover from the anesthesia and a CT scan showed an accumulation of air in the bifrontal subdural space compressing the brain posteriorly.(ABSTRACT TRUNCATED AT 250 WORDS)