The authors present a case of post-traumatic tension pneumocephalus of delayed onset. A 23-year-old man fell down and was admitted to our hospital with initial diagnosis of basal skull fracture associated with small amounts of pneumocephalus on brain computerized tomography(CT). At admission, the consciousness was alert without focal neurological deficit. During conservative therapy, headache was slowly progressive and consciousness became drowsy on 13th day after admission. The brain follow-up CT showed huge low air density lesion in the right frontal area. We performed unilateral subfrontal craniotomy with duroplasty for removal of air and dural repair with galea aponeurotica and abdominal fat. Postoperatively, the condition was recovered.