Mechanisms of action of estrogen on brain structure and function provide biological plausibility for the purported effects of this steroid hormone on aspects of cognition in women. Prospective experimental studies and observational studies indicate that estrogen helps maintain verbal and, possibly, visual memory in women. A suggested battery of neuropsychological tests is presented while caveats concerning possible experimental confounds in studies of estrogen and memory such as depression and the concomitant administration of progestins are discussed. The use of hormone replacement therapy (HRT) in postmenopausal women must also consider the risks and benefits of such treatment for each individual woman.