OBJECTIVE: To review and critically analyze the biological plausibility of and the clinical empirical evidence concerning a link between estrogen levels and memory in women. DATA SOURCES: MEDLINE search of the literature published from 1980 to 1998. Studies published between 1952 and 1980 that were known to the author were also included. STUDY SELECTION: Sixteen prospective, placebo-controlled studies in humans. DATA SYNTHESIS: Most of the studies that used neuropsychological tests with known reliability and validity found that estrogen maintained aspects of memory in women. CONCLUSIONS: Estrogen specifically maintains verbal memory in women and may prevent or forestall the deterioration in short- and long-term memory that occurs with normal aging. There is also evidence that estrogen decreases the incidence of Alzheimer disease or retards its onset or both.