Cerebro/cardiovascular (CV) death accounts for approximately 30% of total deaths in Japan and therefore it is important to establish a preventive treatment for CV events from the point of public health. The guidelines proposed by a joint study group centering on the Japanese Circulation Society, recommend administration of aspirin to patients with multiple risk factors for primary prevention of arteriosclerotic diseases. In addition, the 2002 AHA guidelines recommend use of aspirin in patients with a 10% or higher 10-year risk of CV events. However, these descriptions are founded on randomized, comparative study results and epidemiological data obtained outside Japan, while no epidemiological data are available in Japan that would allow prediction and selection of patients who could benefit from primary prevention with aspirin. Although the benefit of aspirin for secondary prevention has been proven in Japanese patients, the benefits of primary prevention are still controversial.