Background Until now, large-scale nationwide surveys of acute myocardial infarction (AMI), such as those performed in Europe and America, have not been performed in Japan. Therefore, in 2000 the Japanese Coronary Intervention Study (JCIS) group conducted a nationwide survey on the incidence of AMI in Japan. Methods and Results Questionnaires were collected from 8,268 facilities throughout Japan. The total annual number of patients with AMI was 66,459 (52.4 patients/10⁵ population), and the AMI incidence rate in Japan was approximately 25% of that in the United States. Most facilities with AMI patients treated less than 50 AMI patients annually, and that number was 45.0% of total AMI patients. The incidence of AMI patients was highest in Kochi, Kumamoto, and Wakayama prefectures, and lowest in Yamanashi, Saitama and Shiga prefectures. The ratio of the highest incidence to the lowest incidence was 2.0. A significant correlation was observed between the mean age of the prefectural population, as a coronary risk factor, and the incidence of AMI. Conclusions The incidence of AMI in Japan is approximately 25% that in the United States and it varies considerably among the prefectures, one of the causes being the difference in the mean age. This provides important information for assessing the guidelines for Japanese patients with AMI. (Circ J 2004; 68: 515 - 519)