Histopathological change of the pituitary gland in cases of the central nervous system disorder, especially in the cases of subarachnoid hemorrhage, was studied. Clinical materials were 23 cases who were died from subarachnoid hemorrhage due to aneurysmal rupture in the acute stage. Histopathological change was examined not only of the pituitary gland but also hypothalamus and the change due to increased intracranial pressure (midbrain hemorrhage and uncal herniation). Main histopathological findings of the pituitary gland are anterior pituitary necrosis and they are found in 8 cases out of 23 subarachnoid hemorrhage cases (34.9%). Histopathological changes in hypothalamus were hemorrhage or infarction, and these changes were present in 16 cases (70%). Eight cases with pituitary necrosis had shown hypothalamic lesions. Three cases out of 23 cases (17.4%) showed midbrain hemorrhage and uncal herniation and 3 cases out of these 4 cases had anterior pituitary necrosis. According to the angiographic findings, vasospasm tended to be severe and widespread in cases of anterior pituitary necrosis, meanwhile vasospasm did not tend to be severe or widespread in cases without anterior pituitary necrosis. It was suspected that the mechanism of the development of pituitary necrosis is related not only to the circulatory disturbance of the portal vessels due to mechanical compression on the pituitary stalk and acutely raised intracranial pressure at the moment of aneurysmal rupture, but also circulatory disturbance of the portal vessels due to vasospasm.