Most studies reporting bleedings in patients with ST-segment elevation myocardial infarction (STEMI) are reports from clinical trials, which may be unrepresentative of incidences in real-life. In this study, we investigated 1-year bleeding and mortality incidences in an unselected STEMI population, and compared participants with nonparticipants of a randomized all-comer clinical trial (The Third DANish Study of Optimal Acute Treatment of Patients with STEMI (DANAMI-3)). Hospital charts were read and bleedings classified according to thrombolysis in myocardial infarction (TIMI) and Bleeding Academic Research Consortium (BARC) criteria in 2,490 consecutive STEMI patients who underwent primary percutaneous coronary intervention in a single, large, and tertiary heart center. Thrombolysis in myocardial infarction minor and/or major bleeding (TMMB) occurred in 4.4% day 0 to 30 and 2.1% day 31 to 365. DANAMI-3 nonparticipants (n = 887) had significantly higher 30-day bleeding rates than DANAMI-3-participants (n = 1,603) (7.2% vs 2.9%, p <0.0001), but not thereafter (p = 0.8). DANAMI-3 nonparticipation was significantly associated with 30-day TMMB (hazard ratio, 1.8, 95% confidence interval, 1.2 to 2.8, p = 0.007), but this did not persist after adjusting for resuscitated cardiac arrest, Killip-class>2 and anemia. Patients with cardiac arrest, Killip-class>2, and anemia accounted for 70.0% of 30-day TMMBs, and the majority of these patients were DANAMI-3 nonparticipants. TMMB day 0 to 30 was associated with increased 30-day mortality (hazard ratio 3.1, 95% confidence interval 1.9 to 5.2, p <0.0001) but not thereafter (p = 0.9). In conclusion, we found that clinical trial (DANAMI-3) nonparticipants had significantly more TMMBs within 30 days than participants. Patients with resuscitated cardiac arrest, anemia, and Killip-class>2 were accountable for a high rate of TMMBs. Bleeding incidences from clinical trials cannot be translated to an unselected STEMI population.