A case of pituitary apoplexy causing pituitary hemorrhage with extension into the third ventricle is reported. The patient was a 73-year-old, obese female admitted with sudden onset of vomiting and impaired consciousness. Neurological examination revealed that she was stuporous, with marked neck stiffness and a dilated left pupil. A plain skull X-ray showed sellar enlargement and destruction of the dorsum sellae. Computed tomography demonstrated a high-density area in the third and lateral ventricles and a round, high-density mass in the suprasellar cistern. The patient died the next day. Autopsy revealed a large tumor in the sellar and suprasellar areas. The tumor and the hematoma within it compressed the floor of the third ventricle and passed through the lamina terminalis and the hypothalamic region. Histological examination disclosed a basophilic adenoma. The pituitary hemorrhage appeared to be the result of ischemia and necrosis within the pituitary adenoma caused by its acute expansion. The extension of the hematoma into the third ventricle was attributable to the large size of the tumor and its close adhesion to the floor of the third ventricle.