The steady increase in female life expectancy has attracted attention to the importance of preventing cognitive aging and Alzheimer's disease (AD) in women. Evidence from randomized, controlled trials and from cross-sectional and longitudinal studies shows that estrogen-replacement therapy preferentially protects against a decline in verbal memory in healthy postmenopausal women and decreases the risk of AD. Although results are not consistent across studies, they indicate that treatment with estrogen during the postmenopausal years might protect against cognitive aging in women during the latter part of their life.