A 72-year-old man who had undergone a lumboperitoneal shunt for idiopathic normal pressure hydrocephalus was admitted to our emergency department with fever and disturbance of consciousness 8 days after placement. Computed tomography scan showed pneumocephalus and a right-sided temporal porencephalic cyst with a small bone defect in the right petrous bone. Shunt valve pressure was raised from 145 mmH2O to "virtual off" setting. After 2 weeks, follow-up computed tomography showed improvement of pneumocephalus, and the shunt valve pressure was lowered to 215 mmH2O. Since that time, the patient has a good clinical course without recurrence. Tension pneumocephalus following shunt placement for idiopathic normal pressure hydrocephalus is rare and has never been reported in the early postoperative stage after lumboperitoneal shunt, except for the present one. Temporary raising shunt valve pressure is effective in improving the pneumocephalus. Preoperative screening for congenital bone defects by thin-slice computed tomography may be useful for selecting types of shunt valve and determining postoperative pressure setting.