Abstract Background Management of patients with ST-segment elevation myocardial infarction (STEMI) treated with primary percutaneous coronary intervention (PCI) has changed during the last two decades. Introduction of more potent platelet inhibitors may carry an increased risk of bleeding complications, while other therapeutic options, such as use of radial artery access and proton pump inhibitors may reduce bleeding risk. The combined impact of these treatment changes on bleeding risk in patients with STEMI remains unknown. Purpose To examine temporal trends in 1-year risk of major bleeding after STEMI treated with primary PCI from 2003 to 2017. Methods We used the Western Denmark Heart Registry to identify first-time PCI-treated patients undergoing primary PCI for STEMI from 2003 to 2017. Patients were divided into 4 calendar periods based on the time of STEMI. The main outcome was 1-year risk of major bleeding defined as a hospital admission for bleeding using a validated definition with high accuracy. Additionally, the 1-year risk of major bleeding in STEMI patients was compared with the risk in an age- and sex-matched general population cohort without prior coronary artery disease. Results From 2003 to 2017, we identified 18,540 patients treated with primary PCI for STEMI (median age 64 years, 75% men)and 92,700 age- and sex-matched individuals. The 1-year risk of major bleeding after STEMI was similar across the different time periods; 4.1% in 2003-2006, 3.8% in 2007-2010, 3.8% in 2011-2014, and 4.5% in 2015-2017. The adjusted HR for bleeding in STEMI patients was 1.03 (95% CI 0.83-1.26) when comparing the latest period with the earliest period. The age- and sex-matched general population exhibited a 1-year risk of major bleeding of around 1% in all time periods (Figure 1). Conclusions Despite changes in management, the 1-year risk of major bleeding remained stable around 4% after primary PCI-treated STEMI from 2003 to 2017. This risk was approximately 4 times higher than the bleeding risk observed in an age- and sex-matched general population.