That there may be a familial factor in the occurrence of intracranial aneurysm is a possibility that has not yet been advanced, to the knowledge of the authors. It has now been widely accepted that they are of a congenital nature, and, while it does not necessarily follow that they are also familial, it is intriguing to suppose that with further attention to the possibility such a relationship might be discovered. As early as 1887 Eppinger1proposed that aneurysmal sacs might be considered congenital. In 1928 Green2entitled an article "Congenital Aneurysms of the Cerebral Arteries." Dandy3stated that most of the intracranial aneurysms were generally accepted as of congenital origin. More recently, Sugar,4referring to the monograph of Padget,5has been able to point out residuals of embryonic arteries capable of expanding into intracranial aneurysms at their common sites. On the other hand, reports