The prevention of dementia, and particularly of Alzheimer's disease, is a major challenge for researchers and clinicians. In this article, the mixture of evidence, observations and hypotheses in the current literature is categorized into four avenues for possible preventive interventions, as suggested by the NIH State-of-the-Science Conference. The main categories are: antihypertensive medications; nutrition; cognitive engagement; and physical activity. There is, as yet, no conclusive evidence, but each category may hold promise for the prevention of dementia. The robust findings are as follows: cognitive engagement and regular physical activity may reduce the risk of Alzheimer's disease; the Mediterranean diet and consumption of omega-3 fatty acids deserves further elucidation; and the meticulous management of risk factors, and especially hypertension, is the infrastructure of Alzheimer's disease prevention.