OBJECTIVE: To provide health care providers, patients, and the general public with a responsible assessment of currently available data on prevention of Alzheimer's disease and cognitive decline. PARTICIPANTS: A non-Department of Health and Human Services, nonadvocate 15-member panel representing the fields of preventive medicine, geriatrics, internal medicine, neurology, neurological surgery, psychiatry, mental health, human nutrition, pharmacology, genetic medicine, nursing, health economics, health services research, family caregiving, and a public representative. In addition, 20 experts from pertinent fields presented data to the panel and conference audience. EVIDENCE: Presentations by experts and a systematic review of the literature prepared by the Duke University Evidence-based Practice Center, through the Agency for Healthcare Research and Quality. Scientific evidence was given precedence over anecdotal experience. CONFERENCE PROCESS: The panel drafted its statement based on scientific evidence presented in open forum and on published scientific literature. The draft statement was presented on the final day of the conference and circulated to the audience for comment. The panel released a revised statement later that day at http://consensus.nih.gov. This statement is an independent report of the panel and is not a policy statement of the NIH or the Federal Government. CONCLUSIONS: Cognitive decline and Alzheimer's disease are major causes of morbidity and mortality worldwide and are substantially burdensome to the affected persons, their caregivers, and society in general. Extensive research over the past 20 years has provided important insights on the nature of Alzheimer's disease and cognitive decline and the magnitude of the problem. Nevertheless, there remain important and formidable challenges in conducting research on these diseases, particularly in the area of prevention. Currently, firm conclusions cannot be drawn about the association of any modifiable risk factor with cognitive decline or Alzheimer's disease. Highly reliable consensus-based diagnostic criteria for cognitive decline, mild cognitive impairment, and Alzheimer's disease are lacking, and available criteria have not been uniformly applied. Evidence is insufficient to support the use of pharmaceutical agents or dietary supplements to prevent cognitive decline or Alzheimer's disease. We recognize that a large amount of promising research is under way; these efforts need to be increased and added to by new understandings and innovations (as noted in our recommendations for future research). For example, ongoing studies including (but not limited to) studies on antihypertensive medications, omega-3 fatty acids, physical activity, and cognitive engagement may provide new insights into the prevention or delay of cognitive decline or Alzheimer's disease. This important research needs to be supplemented by further studies. Large-scale population-based studies and randomized controlled trials (RCTs) are critically needed to investigate strategies to maintain cognitive function in individuals at risk for decline, to identify factors that may delay the onset of Alzheimer's disease among persons at risk, and to identify factors that may slow the progression of Alzheimer's disease among persons in whom the condition is already diagnosed.