For acute myocardial infarction (AMI), "weekend" has been associated with higher incidence, admission, and fatality. But, very few studies in this regard are available in Japan. Day of the week variation in AMI was examined using an entire community covering 16-year AMI registration data from Japan. Data were obtained from the Takashima AMI Registry, which covers a stable population of approximately 55,000 in central Japan. There were 379 registered first ever AMI cases with 121 fatal events within 28 days of onset during 1988-2003. We divided the days into two groups: 'Weekend' (Saturday and Sunday) and 'Weekdays' (Monday to Friday). The incidence rate (per 100,000 person-year), admission rate (per 1,000 days) and 28-day case-fatality rates (per 100 events) as well as corresponding rate ratios were calculated with 95% confidence intervals. The distribution of the day of the week for onset, admission and fatality for all subjects was fairly random in our study population; incidence (chi (2) test, P = 0.8), admission (chi (2) test, P = 0.9) and case-fatality (chi (2) test, P = 0.8). The incidence, admission, and case-fatality rates were similar for the 2 day-groups. The incidence rate ratio 1.06 (95% CI: 0.9-1.3), admission ratio 1.03 (95% CI: 0.8-1.3), and case-fatality ratio 1.18 (95% CI: 0.7-1.9) showed no significant risk difference between weekend and weekday. After various adjustments, hazard ratio for weekend AMI in reference to weekday AMI was 1.07 (95% CI: 0.5-2.1). There were no obvious differences in occurrence, hospital admission and acute outcome for AMI patients in the weekday or weekend.