Promising results from observational studies suggest that hormone replacement therapy (HRT) attenuates age-related cognitive decline and decreases the risk of Alzheimer's disease. However, results from Women's Health Initiative Memory Study (WHIMS) clearly demonstrate that conjugated equine estrogen and medroxyprogesterone acetate do not benefit cognitive health in women aged 65 or older. These drugs should not be used to maintain cognitive function in these women. HRT may exert a cognitive benefit in younger postmenopausal women, particularly those reporting menopausal symptoms. Cognitive benefit is most often seen on measures of attention and verbal memory. These impairments of cognitive dysfunction may be among the menopausal symptoms ameliorated by HRT in some women. It would be clinically prudent to prescribe HRT only for its approved indications and to caution younger women initiating HRT about the WHIMS findings. Further research is needed on the effects of timing of HRT and on the cognitive effects of other hormone preparations, doses, modes of administration, and effects of the various progestational agents used in combination therapy.