['Studies from North America indicate that patients admitted during the weekend with acute myocardial infarction (AMI) have a worse outcome than weekday-admitted patients, probably reflecting a lower rate of invasive procedures. However, it is unclear whether the same is true in Japan, which has a different healthcare system.', 'Using the Japanese Acute Coronary Syndrome Study (JACSS) database, this study included 4,805 consecutive patients who were admitted within 48 h of onset of AMI (3,526 [73.4%] patients with weekday onset [Monday through Friday] and 1,279 [26.6%] with weekend onset [Saturday and Sunday]). There were no significant differences between the 2 groups in patient background and clinical features. The proportions of patients who underwent emergency catheterization (88.4% vs 88.0%) and reperfusion therapy (81.5% vs 81.4%) were also similar. There were no differences between the 2 groups in the in-hospital, 30-day, and 1-year mortality rates. Even after various adjustments, there was no difference in the risk of death associated with weekend versus weekday onset of AMI.'] Does weekend onset of acute myocardial infarction have a negative impact on outcome in Japan?