Despite the classic presentation of aSAH, individual find- ings occur inconsistently, and because the type of headache from aSAH is sufficiently variable, misdiagnosis or delayed diagnosis is common. Before 1985, misdiagnosis of aSAH occurred in as many as 64% of cases, with more recent data suggesting a misdiagnosis rate of 12%.89,90 Misdiagnosis was associated with a nearly 4-fold higher likelihood of death or disability at 1 year in patients with minimal or no neurological deficit at the initial visit.89 The most common diagnostic error is failure to obtain a noncontrast head CT scan.89,91 93 In a small subset of patients, a high degree of suspicion based on clinical presentation will lead to the correct diagnosis despite normal head CT and cerebrospinal fluid test results, as shown in a recent study in which 1.4% of patients were diagnosed with aSAH only after vascular imaging techniques were used.94 Patients may report symptoms consistent with a minor hemorrhage before a major rupture, which has been called a sentinel bleed or warning leak.83,84 The majority of these minor hemorrhages occur within 2 to 8 weeks before overt aSAH. The headache associated with a warning leak is usually milder than that associated with a major rupture, but it may last a few days.95,96 Nausea and vomiting may occur, but meningismus is uncommon after a sentinel hemorrhage. Among 1752 patients with aneurysm rupture from 3 series, 340 (19.4%; range, 15% 37%) had a history of a sudden severe headache before the event that led to admission.82,95,97 The importance of recognizing a warning leak cannot be overemphasized. 