Multiple factors appear to contribute to the expression of Alzheimer's disease (AD). About 30% of cases of dementia of the Alzheimer's type (DAT) can be attributed to genetic factors. These observations raise the possibility of identifying multiple interventions that may modify the disease process and, therefore, the clinical expression of the dementia. Prominent among factors that may contribute to dementia and, specifically, to dementia of the Alzheimer's type is cerebral vascular disease. Estrogen is a potent factor that not only prevents vascular disease but also improves blood flow in diseased vessels, including blood flow in regions of the brain affected by AD. Estrogen also has direct effects on neuronal function that may play an important role not only in the preservation of neurons but in the repair of neurons damaged by the disease process. These effects of estrogen on the CNS suggest that the hormone may be effective not only in the prevention of dementia but also in its treatment. Given the distressingly high prevalence of AD among older women and the exorbitant social and economic costs associated with this disorder, a true risk reduction on the order of one-third to one-half, as suggested by several recent analytical studies, would be of tremendous public health importance.