The simultaneous occurrence of cancer and coronary heart disease is increasing in the Western world. Nevertheless, the influence of cancer on ST elevation myocardial infarction (STEMI) treated with primary percutaneous coronary intervention (PCI) has not been investigated extensively. This multicenter registry included patients with STEMI treated with primary PCI from 2006 to 2009. Patients were stratified according to history of cancer, and primary focus lay on all-cause and cardiac mortalities during 1-year follow-up. Adjusted effect sizes were calculated using Cox proportional hazard models. In total, 208 patients had a history of cancer (diagnosed ≤6 months ago in 20.7%, 6 months to 3 years ago in 21.7%, and >3 years ago in 57.6%) and 3,215 patients had no history of cancer. Chemotherapy had been administered previously to 23% of patients with cancer. Patients with cancer were older, more frequently women, and more commonly known with previous myocardial infarction or anemia. Reperfusion rates were similar after PCI. Patients with cancer showed greater all-cause (17.4% vs 6.5% in other patients) and cardiac mortalities at 1 year (10.7% vs 5.4% in other patients) because of high early cardiac death (23.8%) in recently diagnosed patients with cancer. After adjustment, a recent cancer diagnosis predicted cardiac mortality at 7 days (hazard ratio 3.34, 95% confidence interval 1.57 to 7.08). The adverse prognosis was partly explained by anemia and occurrence of cardiogenic shock, whereas outcome was independent of cancer treatment. In conclusion, patients with cancer showed greater mortality after STEMI. A cancer diagnosis in the 6 months before primary PCI was strongly associated with early cardiac mortality.