ObjectiveSex differences in the association between cardiovascular risk factors and the incident all‐cause dementia and the subtype Alzheimer's disease (AD) risk are unclear.MethodsFramingham Heart Study (FHS) participants (n = 4,171, 54% women, aged 55 to 69 years) were included at baseline and followed up to 40 years. The Framingham Stroke Risk Profile (FSRP) was dichotomized into 2 levels (cutoff: 75th percentile of the FSRP z‐scores). Cause‐specific hazard models, with death as a competing event, and restricted mean survival time (RMST) model were used to analyze the association between FSRP levels and incident all‐cause dementia and AD. Interactions between FSRP and sex were estimated, followed by a sex‐stratified analysis to examine the sex modification effect.ResultsHigh FSRP was significantly associated with all‐cause dementia (hazard ratio [HR] = 1.25, robust 95% confidence interval [CI] = 1.21 to 1.29, p < 0.001) and AD (HR = 1.58, robust 95% CI = 1.57 to 1.59, p < 0.001) in cause‐specific hazard models. High FSRP was significantly associated with incident dementia (HR = 2.81, robust 95% CI = 2.75 to 2.87, p < 0.001) and AD (HR = 2.96, robust 95% CI = 2.36 to 3.71, p < 0.001) in women, but not in men. Results were consistent in the RMST models. Current diabetes and high systolic blood pressure as FSRP components were significantly associated with dementia and AD in women but not in men.InterpretationHigh FSRP in mid‐ to early late life is a critical risk factor for all‐cause dementia and AD, particularly in women. Sex‐specific interventions and further research to elucidate underlying mechanisms are warranted. ANN NEUROL 2024;96:1124–1134