None of the published studies that have related physical activity (PA) exposures with stroke outcomes have included a representative population sample, none have used objective measures of PA, and none have been specifically designed to examine racial or geographical variations in PA patterns and stroke incidence. In this application we propose an ancillary study to examine PA patterns and stroke risk in a racially and geographically diverse population sample of nearly 22,000 free-living women and men enrolled in the Reasons for Geographic and Racial Differences in Stroke (REGARDS) Study. REGARDS, managed by investigators at the University of Alabama at Birmingham, is a recently initiated prospective study funded by National Institute of Neurological Disorders and Stroke. The focus of the proposed ancillary study (i.e., REGARDS-PA) will be to quantify usual ambulatory PA patterns in terms of frequency, duration and intensity, and thus, the total dose of activity-related minutes and energy expenditure (EE). PA exposures will be related with the occurrence of stroke events and the degree to which these associations are confounded or modified by sex, race, geographical location, and conventional CVD risk factors. Strengths of the study will be the large population sample of racially and geographically diverse adults broadly representative of the overall U.S. population 45 years of age and older, use of objectively-measured PA from an electronic accelerometer, access to extensive baseline data on personal and family health histories, CVD risk predictors including plasma markers and selected physical measurements, 5-year surveillance for stroke events at 6-month intervals, and confirmation of incident stroke events and other study endpoints by medical record review. Findings from this study will provide empirical evidence of the role that variation in PA levels has on differences in stroke occurrence among population subgroups as defined by race and geographic region, which could have important clinical and public health implications for enhancing health-related PA recommendations and for improving population based stroke prevention strategies. REGARDS is also uniquely positioned to provide insights to the first national data on predictors of cognitive change. Because cognitive function, which in many instances is directly impacted by stroke, also will be recorded regularly during the follow-up period, the opportunity exists to expand on the primary analyses to investigate whether any variations in this clinical outcome are explained by variations in PA. Additionally, the dose-response relationship between PA and cognitive function will be explored with greater accuracy than any other previous longitudinal study due to the objective measurement of PA. Such data will be critical in developing effective PA recommendations to maintain optimal cognitive function during aging. This is much needed considering the overall aging of the U.S. population and strong importance American adults place on maintaining brain health as they age.