Tension pneumocephalus is a serious and life-threatening complication after craniotomy, and many cases have been reported after craniotomy in the sitting position. The definitive treatment is the surgical aspiration of air via burr holes. We report two cases of tension pneumocephalus after craniotomy in the supine position, whose neurological status improved prior to the surgical intervention. One patient with metastatic brain tumor in the left frontoparietal lobe was operated on for the removal of the tumor in the supine position under neuroleptanesthesia. After the operation, the patient showed a delayed recovery, and an emergency CT scan revealed a large amount of bilateral subdural air. The other with infiltrating pituitary tumor was undewent the right frontotemporal craniotomy for the removal of the tumor under nitrous oxide and enflurane anesthesia. After full awakening from anesthesia, gradual deterioration in the neurological status needed an emergency CT scan, which showed air in the right frontotemporal epidural space with the midline shift to the left. The neurological status of the two patients improved fortunately prior to the surgical intervention, while receiving intravenous mannitol and steroids with continuous inhalation of oxygen. The postoperative repeated CT scans taken after one week showed only minimal cerebral edema without definite accumulation of air in both cases.