The author reports on 41 aneurysms of the proximal internal carotid artery (PICA) demonstrated in 36 patients with subarachnoid hemorrhage. The patients included a striking preponderance of women, and there was a high incidence of multiple aneurysms. In cases with multiple aneurysms the PICA aneurysm was usually found incidentally, a more distal aneurysm on the internal carotid artery being the source of hemorrhage. An infundibulum at the origin of a posterior communicating artery was unusually common in these patients. The origin of the ophthalmic artery is proposed as the angiographic landmark of the level at which the internal carotid artery penetrates the dura mater.