Diabetes mellitus (DM) is a chronic disease with high prevalence rate, mortality rate and socioeconomic burden. Management of DM is becoming an important issue in the society. According to the guidelines, prescription of Aspirin is recommended to reduce the risk of cardiovascular diseases (CVDs) in DM patients. However, the risk-benefit assessment (risk of bleeding and prevention of CVDs) has been raised in debate recently and in 2010, updated guidelines narrow down the limit of the aspirin recommendation for primary prevention of CVDs. However, there is not enough relevant data in Korea. This study was performed to evaluate the effectiveness of low dose aspirin use in preventing CVDs in newly diagnosed diabetic patients.