This application seeks funding for a randomized double-blind placebo-controlled trial of aspirin in primary prevention in healthy elderly people aged 70 years and over. Its purpose is to determine whether low dose aspirin will extend the duration of disability-free life in an aging population. The study will examine whether the potential benefits of this drug (particularly the prevention of heart disease, stroke and vascular dementia) outweigh the risks of severe bleeding in this age group. 19,000 participants will be recruited from community settings in the United States and Australia and randomized to daily 100 mg of enteric-coated aspirin or placebo. Follow-up is for an average of 5 years. The trial methods are based around the successful conduct of large-scale clinical outcome studies in both countries, e.g., ALLHAT, 2nd Australian National Blood Pressure study. The ASPREE study accords with the first of the four major goals of the National Institute of Aging - "to improve the health and quality of life of older people". The Action Plan for Aging Research of the NIA points out that since the beginning of the 20th century, life expectancy at birth in the U.S. has increased from less than 50 years to more than 76 years. From 1960 to 2000 there was an approximate doubling of people aged 65 and over. It is further predicted that by the year 2030, the number of individuals aged 65 and over will double again to reach 70.3 million (constituting 20% of the population). Dramatic growth in the elderly population is also predicted in the number of Americans aged 85 and over to reach 19.4 million (4.8% of the population in 2050). As life expectancy increases, there is now a greater need to keep these additional years free of disease and disability. At present, the use of aspirin for primary prevention is based largely on studies in middle aged adults where the incidence of adverse affects is low. However, the risk benefit ratio of this agent in older persons is an area of continuing controversy. This is reflected by incorporating aspirin therapy into some widely respected clinical guidelines, despite the failure of the FDA cardio-renal Drugs Panel to endorse its use in this setting. The result of the ASPREE aspirin study will have the potential to alter clinical practice for the majority of the older U.S. population where approximately 60% of those over 65 are free of heart disease, stroke and mental or physical disability. Its relevance is enhanced by the data suggesting that aspirin may delay the onset of cognitive decline and some forms of cancer. However, recent experience with other major drug therapies newly introduced, e.g., HRT, COX-2 inhibitors and anti-oxidant vitamins, has emphasized the need to formally establish safety and efficacy before such therapies enter routine practice.