Hypopituitarism may be caused by a variety of lesions, mostly interfering with pituitary blood flow. Kernohan and Sayre (1956) list many causes both within and around the sella turcica that lead to hypopituitarism, including granulomas, metastatic carcinoma, extension of a carcinoma of the nasopharynx, chordomas, and meningiomas, arising from the crest between the anterior clinoid processes, which by growing downwards toward the pituitary compress it with resultant hypopituitarism. In their comprehensive survey of such causes, no mention is made of intracranial arterial aneurysms occupying the sella and simulating a hypophyseal tumor. However, White and Ballantine (1961) have described three patients in whom an original diagnosis of a pituitary adenoma was corrected after carotid arteriography to one of intracranial aneurysm compressing the pituitary gland. In addition these authors reviewed the 19 previously published case histories of the same condition and analyzed a further 13 submitted to them by several neurosurgeons.