Expert peer review of AHA Scientific Statements is conducted by the AHA Office of Science Operations. For more on AHA statements and guidelines development, visit http://my.americanheart.org/statements and select the Policies and Development link. Permissions: Multiple copies, modification, alteration, enhancement, and/or distribution of this document are not permitted without the express permission of the American Heart Association. Instructions for obtaining permission are located at http://www.heart.org/HEARTORG/General/ Copyright-Permission-Guidelines_UCM_300404_Article.jsp. A link to the Copyright Permissions Request Form appears on the right side of the page. This statement was approved by the American Heart Association Science Advisory and Coordinating Committee on January 30, 2012. A copy of the document is available at http://my.americanheart.org/statements by selecting either the By Topic link or the By Publication Date link. To purchase additional reprints, call 843-216-2533 or e-mail kelle.ramsay@wolterskluwer.com. 2012 American Heart Association, Inc. Stroke is available at http://stroke.ahajournals.org DOI: 10.1161/STR.0b013e3182587839 To respond to the growing call for more evidenced-based medicine, the American Heart Association (AHA) com- missions guidelines on various clinical topics and endeavors to keep them as current as possible. The prior aneurysmal subarachnoid hemorrhage (aSAH) guidelines, sponsored by the AHA Stroke Council, were previously issued in 19941 and 2009.2 The 2009 guidelines covered literature through No- vember 1, 2006.2 The present guidelines primarily cover literature published between November 1, 2006, and May 1, 2010, but the writing group has strived to place these data in the greater context of the prior publications and recommen- dations. In cases in which new data covered in this review have resulted in a change in a prior recommendation, this is explicitly noted. aSAH is a significant cause of morbidity and mortality throughout the world. 