ALTHOUGH not considered common, multiple intracranial arterial aneurysms occur with sufficient frequency to preclude the possibility that they represent merely rare coincidental abnormalities. Dandy1estimated that approximately 15% of cases of intracranial aneurysms were multiple, and Hamby2gave some consideration to their clinical and pathologic significance. Otherwise little more than casual notice has been made of them except as occasional case reports and incidental findings in statistical analyses. Even the exhaustive tabulation of intracranial aneurysms compiled by McDonald and Korb3is generally limited to a listing of but one, when multiple aneurysms were present. If there was rupture of one of them, it was the one listed. Hence an analysis and review of intracranial aneurysms in terms of the significance of their multiplicity appears timely. The earliest known reference to the subject of intracranial aneurysms was made in 1761 by Morgagni,* who described intracranial arterial dilatations, presumably