The term spontaneous subarachnoid hemorrhage is used in this contribution to designate massive extravasation of blood into the subarachnoid space, caused by spontaneous rupture of a blood vessel. Thus, by definition, the term excludes other forms of bleeding into the subarachnoid space, such as those provoked by trauma causing laceration of brain tissue and blood vessels, those occurring in the course of some systemic disease and those that are but extensions of a massive intracerebral hemorrhage in which disruption of brain tissue allows a direct escape of blood into the subarachnoid space. Following the classic description by Bramwell1of the so-called spontaneous meningeal hemorrhage, numerous contributions have been made on the subject, but they, aside from the comprehensive communication of Symonds2and the more recent one by Mclver and Wilson,3consist mainly of case reports which add little to the early and excellent clinical observations recorded by