BACKGROUND: Cardiovascular disease and vascular risk factors increase rates of cognitive impairment, but very little is known regarding prevention in this high-risk group. The heart-healthy Mediterranean-type dietary pattern may beneficially influence both vascular and cognitive outcomes. OBJECTIVES: We examined the association between Mediterranean-style diet and cognitive decline in women with prevalent vascular disease or ≥3 coronary risk factors. DESIGN/PARTICIPANTS/SETTING: Prospective cohort study among 2,504 women participants in the Women's Antioxidant Cardiovascular Study (WACS), a cohort of female health professionals. Adherence to a Mediterranean-style diet was determined at WACS baseline (1995-1996) using a 0- to 9-point scale with higher scores indicating higher adherence. In 1998-2000, participants aged ≥65 years underwent a telephone cognitive battery including five tests of global cognition, verbal memory, and category fluency. Tests were administered three additional times across 5.4 years. STATISTICAL ANALYSES PERFORMED: We used multivariable-adjusted generalized linear models for repeated measures to compare the annual rates of cognitive score changes across tertiles of Mediterranean diet score, as assessed at WACS baseline. RESULTS: In both basic- and multivariable-adjusted models, consuming a Mediterranean-style diet was not related to cognitive decline. No effect modification was detected by age, education, depression, cardiovascular disease severity at WACS baseline, or level of cognition at initial assessment. CONCLUSIONS: In women at higher risk of cognitive decline due to vascular disease or risk factors, adherence to a Mediterranean-style diet was not associated with subsequent 5-year cognitive change.