Relatively few women were enrolled in the primary preven- tion trials that showed a benefit of aspirin in the prevention of coronary heart events but no reduction in stroke. The WHS randomized 39876 initially asymptomatic women 45 years of age to receive 100 mg aspirin on alternate days or placebo and followed them up for 10 years for a first major vascular event (nonfatal MI, nonfatal stroke, or cardiovascular death).889 Unlike data from earlier studies that included mainly men, this study found a nonsignificant 9% reduction (RR, 0.91; 95% CI, 0.80 1.03; P=0.13) for the combined primary end point among women but a 17% reduction in the risk of stroke (RR, reduction in the risk of ischemic stroke (RR, 0.76; 95% CI, 0.63 0.93; P=0.009) and a nonsignificant increase in the risk of hemorrhagic stroke (RR, 1.24; 95% CI, 0.82 1.87; P=0.31). The overall average stroke rates were 0.11%/y in aspirin- treated women and 0.13%/y in placebo-treated women (RR, 0.02%/y; number needed to treat, 5000). Gastrointestinal hem- orrhage requiring transfusion was more frequent in the aspirin gastrointestinal hemorrhage rates were 0.06%/y for aspirin and 0.05%/y for placebo (absolute risk increase, 0.01%/y; num- ber needed to harm, 10000). The most consistent benefit for aspirin was in women 65 years of age at study entry, among whom the risk of major cardiovascular events was reduced a 30% reduction in the risk of ischemic stroke (RR, 0.70; 95% CI, 0.49 1.00; P=0.05); however, there was only a trend in the reduction of the overall risk of all types of stroke (RR, 0.78; 95% CI, 0.57 1.08; P=0.13), likely related to an increase in the risk of brain hemorrhages. 