New European Society of Cardiology/American College of Cardiology guidelines classify patients with acute coronary syndrome and increased cardiac troponins as non–ST-segment elevation myocardial infarction (NSTEMI) who would have been classified as unstable angina pectoris (UAP) using the older World Health Organization (WHO) definition. The optimal revascularization strategy in these patients is poorly defined. This prospective cohort study included 1,024 consecutive patients with acute coronary syndrome classified as UAP, NSTEMI according to the WHO definition (WHO NSTEMI), and NSTEMI additionally identified by the novel European Society of Cardiology/American College of Cardiology definition (additional NSTEMI). All patients underwent coronary angiography within 24 hours and were treated with immediate percutaneous coronary intervention (PCI) or early coronary artery bypass grafting (CABG). The primary end point was all-cause mortality during follow-up of 36 months. Patients with additional NSTEMI showed excessive cumulative 3-year mortality if undergoing CABG (hazard ratio 5.9, 95% confidence interval 2.7 to 13.1, p <0.001). In patients with UAP or WHO NSTEMI, mortality was similar in the CABG and PCI groups. In conclusion, in the absence of randomized trials specifically including patients with additional NSTEMI, the excessive mortality observed with CABG in this cohort study suggested that PCI may be the preferable revascularization strategy in this subgroup.