We report the first case of postoperative acute subdural hemorrhage following extended transsphenoidal surgery (TSS). The patient was a 74-year-old woman with a cystic suprasellar craniopharyngioma with panhypopituitarism. Extended TSS resulted in complete tumor removal. However her consciousness did not recover well. Emergent computed tomography demonstrated a right acute supratentorial subdural hematoma with impending cerebral herniation. Emergent craniotomy revealed hemorrhage from the vein of Labbé. It may have been caused by acute intracranial hypotension secondary to rapid and massive drainage of cerebrospinal fluid. Surgeons should be aware of the possibility of intracranial hemorrhage as a rare but critical complication of extended TSS.