Although a number of population-based studies have indi- cated that the incidence of aSAH has remained relatively stable over the past 4 decades,5,10 16 a recent review that adjusted for age and sex suggested a slight decrease in incidence between 1950 and 2005 for regions other than Japan, South and Central America, and Finland.4 These data are consistent with studies that show that the incidence of aSAH increases with age, with a typical average age of onset in adults 50 years of age.3,7,17,18 aSAH is relatively uncom- mon in children; incidence rates increase as children get older, with incidence ranging from 0.18 to 2.0 per 100 000.4,19 The majority of studies also indicate a higher incidence of aSAH in women than in men.7,11 13,20 22 Most recent pooled figures report the incidence in women to be 1.24 (95% confidence interval, 1.09 1.42) times higher than in men.4 This is lower than a previous estimate of 1.6 (95% confidence interval, 1.1 2.3) for the years 1960 to 1994.23 Evidence of a sex-age effect on aSAH incidence has emerged from pooled study data, with a higher incidence reported in younger men (25 45 years of age), women between 55 and 85 years of age, and men 85 years of age.4 Differences in incidence of aSAH by race and ethnicity appear to exist. 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). 