Background: Cardiovascular disease (CVD) is a leading cause of death in Japan. To reduce the threat of CVD, it is important to identify its major risk factors. The population attributable fraction (PAF) is calculated from the prevalence and relative risk of risk factors and can be used to estimate the burden of these factors with respect to CVD. We analyzed the findings from several prospective studies to determine the PAFs of CVD. Methods: PAF was calculated as pd × (multiadjusted relative risk - 1)/multiadjusted relative risk, where pd is the proportion of patients exposed to that risk factor category, according to data from the Ohsaki Cohort Study, EPOCHJAPAN, NIPPON DATA80, Miyagi Cohort Study, CARDIA Study, and ARIC Study. Results: Nonoptimal blood pressure explained 47% and 26% of CVD mortality in middle-aged and elderly Japanese, respectively. Cigarette smoking explained 34% of all-cause mortality in middle-aged men. The combination of hypertension and cigarette smoking explained 57% and 44% of CVD mortality in younger men and women, respectively. Furthermore, the presence of at least 1 nonoptimal risk factor explained most CVD deaths and all-cause deaths. Conclusions: Established CVD risk factors, especially high blood pressure and cigarette smoking, explained a large proportion of CVD mortality and all-cause mortality. Prevention, early detection, and treatment of these conventional risk factors are required to reduce mortality risk.