A case is presented in which the sudden onset of bitemporal hemianopsia was caused by partial thrombosis associated with enlargement of an unruptured anterior communicating artery aneurysm. The features of the sequential computed tomographic scans resembled those of pituitary apoplexy, reemphasizing the necessity for cerebral angiography in preoperative evaluation. The clinical significance of the warning signs of cerebral aneurysm during the era of computed tomography is discussed.