Walking speed is a simple, reliable, and valid measure of functional status that has been shown to be strongly correlated with age-related outcomes and may be an indicator of subclinical cerebrovascular disease. However, few studies have investigated the association of walking speed with risk of incident ischemic stroke. The present analyses included 13,048 postmenopausal women (mean age 65 years) from the Women's Health Initiative free of stroke at baseline, 264 of whom had incident ischemic strokes on follow-up. Cox proportional hazards regression was used to obtain hazard ratios (HRs) and 95% confidence intervals (CIs) to assess the relationship between performance on a timed walk and risk of incident ischemic stroke. Multivariate adjustment included age, race/ethnicity, body mass index, waist-hip ratio, depression, arthritis, hypertension, smoking, systolic blood pressure, treated diabetes, hormone use, NSAID use, aspirin use, self-reported general health, and history of coronary heart disease. Slower walking speed was a significant predictor of incident ischemic stroke. After multivariate adjustment, the hazard for incident ischemic stroke was increased for the slowest walking speed tertile compared to the fastest walking speed tertile (HR=1.69, 95% CI: 1.21, 2.36). Additional adjustment for other physical function variables (grip strength and chair stands) did not change the association significantly. Slow walking speed was found to be a strong predictor of increased risk of incident ischemic stroke among postmenopausal women independent of other established risk factors for stroke.