Blacks and Hispanics have a higher incidence of aSAH than Risk Factors for and Prevention of aSAH Behavioral risk factors for aSAH include hypertension, smok- ing, alcohol abuse, and the use of sympathomimetic drugs (eg, cocaine). In addition to female sex (above), the risk of aSAH is increased by the presence of an unruptured cerebral aneurysm (particularly those that are symptomatic, larger in size, and located either on the posterior communicating artery or the vertebrobasilar system), a history of previous aSAH (with or without a residual untreated aneurysm), a history of familial aneurysms (at least 1 first-degree family member with an intracranial aneurysm, and especially if 2 first- degree relatives are affected) and family history of aSAH,26,27 and certain genetic syndromes, such as autosomal dominant polycystic kidney disease and type IV Ehlers-Danlos syn- drome.28,29 Novel findings reported since publication of the previous version of these guidelines include the following: (1) Aneurysms in the anterior circulation appear to be more prone to rupture in patients 55 years of age, whereas posterior communicating aneurysms ruptured more fre- quently in men, and basilar artery aneurysm rupture is associated with lack of use of alcohol.30 (2) The size at which Table 1. Applying Classification of Recommendation and Level of Evidence A recommendation with Level of Evidence B or C does not imply that the recommendation is weak. Many important clinical questions addressed in the guidelines do not lend themselves to clinical trials. Although randomized trials are unavailable, there may be a very clear clinical consensus that a particular test or therapy is useful or effective. *Data available from clinical trials or registries about the usefulness/efficacy in different subpopulations, such as sex, age, history of diabetes, history of prior myocardial infarction, history of heart failure, and prior aspirin use. 