Bleeding events in relation to treatment of ST-segment elevation myocardial infarction (STEMI) have previously been associated with mortality. In this study, we investigated the incidence and prognosis of, and variables associated with serious bleedings within 30 days after primary percutaneous coronary intervention in patients from The Third Danish Study of Optimal Acute Treatment of Patients with ST-Segment Elevation Myocardial Infarction (DANAMI-3) (n = 2,217). Hospital charts were read within 30 days postadmission to assess bleeding events using thrombolysis in myocardial infarction (TIMI) and Bleeding Academic Research Consortium criteria. TIMI minor/major bleeding (TMMB) occurred in 59 patients (2.7%). Variables associated with TMMB were female gender (hazard ratio [HR] 3.9, 95% confidence interval [CI] 2.2 to 6.7, p <0.0001), symptom-to-catheterization time >3 hours (HR 1.9, 95% CI 1.1 to 3.3, p = 0.02), use of glycoprotein IIb/IIIa inhibitor (HR 2.1, 95% CI 1.2 to 3.7, p = 0.01), and increasing S-creatinine (HR 1.1, 95% CI 1.0 to 1.2, p = 0.001). Undergoing 2 in-hospital procedures were not associated with increased risk of TMMB. TMMB was strongly associated with 30-day mortality in multivariable analysis (HR 4.8, 95% CI 2.2 to 10.4, p <0.0001) but not with mortality days 31 to 365. When excluding fatal bleedings from the analysis, a TMMB was no longer associated with 30-day mortality. In conclusion, we found that in a contemporary STEMI-population, the incidence of 30-day TMMB was low. A TMMB was strongly associated with 30-day mortality but not with mortality days 31 to 365. If patients survived a serious bleeding, their short- and long-term prognoses were not affected.