BACKGROUND: Less invasive treatment and poorer outcomes have been shown among patients admitted with acute myocardial infarction (AMI) on weekends compared to weekdays. OBJECTIVES: To investigate the 'weekend-effect' on mortality in patients with AMI. METHODS: Using nationwide registers we identified 92,164 patients aged 30-90years who were admitted to a Danish hospital with a first AMI from 1997 to 2009. Patients were stratified according to weekday- or weekend admissions and four time-periods to investigate for temporal changes. All-cause mortality at 2, 7, 30, and 365days was investigated using proportional hazards Cox regression. RESULTS: Mortality rates were higher on weekends within seven days of admission in 1997-99 (absolute difference ranging from 0.8 to 1.1%). Weekend-weekday hazard-ratios were 1.13 (1.03-1.23) at day 2 and 1.10 (1.01-1.18) at day 7. There were no significant differences in 2000-09 and estimates suggested an attenuation of the initial 'weekend-effect'. Overall, the use of coronary angiography (34.9% vs. 72.3%) and percutaneous coronary intervention (6.6% vs. 51.0%) within 30days increased, as did the use of statins (49.9% vs. 80.1%.) and clopidogrel (26.7% vs. 72.7%). The cumulative mortality decreased during the study period from 5.4% to 2.5% at day of admission, from 19.5% to 11.0% at day 30 and from 28.0% to 19.0% at day 365 (all tests for trend p