The epidemiologic evidence for an association between estrogen and cognitive function among healthy postmenopausal women remains controversial. Equivocal findings may be explained, in part, by differences in the methodologic approaches of these studies. Overall, the evidence for a positive relationship comes primarily from randomized clinical trials. These trials suggest an acute effect on specific tests of recent verbal memory and tasks incorporating concept formation and reasoning. The potential long-term effects of estrogen in slowing or delaying the age-related decline in cognitive function require further study. More data are needed to determine the effects of estrogen replacement therapy on cognitive function, independent of changes in mood and depressive symptoms. In addition, evidence suggests that progesterone may mitigate the beneficial effects of estrogen on mood. Research should be undertaken to determine the interactive effects of estrogen and progesterone on cognitive function. Lastly, there should be continued investigation by both epidemiologic and basic neuroscientific studies to further elucidate the specific cognitive domains that may respond to estrogen.