The safety of the European Society of Cardiology (ESC) 0/1-h algorithm for rapid rule-out and rule-in of non–ST-segment elevation myocardial infarction (NSTEMI) using high-sensitivity cardiac troponin (hs-cTn) has been questioned. This study aimed to validate the diagnostic performance of the 0/1-h algorithm in a large multicenter study. The authors prospectively enrolled unselected patients in 6 countries presenting to the emergency department with symptoms suggestive of NSTEMI. Final diagnosis was centrally adjudicated by 2 independent cardiologists. Hs-cTnT and hs-cTnI blood concentrations were measured at presentation and after 1 h. Safety of rule-out was quantified by the negative predictive value (NPV) for NSTEMI, accuracy of rule-in by the positive predictive value (PPV), and overall efficacy by the proportion of patients triaged towards rule-out or rule-in within 1 h. Prevalence of NSTEMI was 17%. Among 4,368 patients with serial hs-cTnT measurements available, safety of rule-out (NPV 99.8%, 2,488 of 2,493), accuracy of rule-in (PPV 74.5%, 572 of 768), and overall efficacy were high by assigning three-fourths of patients either to rule-out (57%, 2,493 to 4,368) or rule-in (18%, 768 to 4,368). Similarly, among 3,500 patients with serial hs-cTnI measurements, safety of rule-out (NPV 99.7%, 1,528 of 1,533), accuracy of rule-in (PPV 62.3%, 498 of 800), and overall efficacy were high by assigning more than two-thirds of patients either to rule-out (44%, 1,533 of 3,500) or rule-in (23%, 800 of 3,500). Excellent safety was confirmed in multiple subgroup analyses including patients presenting early (≤3 h) after chest pain onset. The ESC 0/1-h algorithm using hs-cTnT and hs-cTnI is very safe and effective in triaging patients with suspected NSTEMI. (Advantageous Predictors of Acute Coronary Syndromes Evaluation APACE; NCT00470587; and Biomarkers in Acute Cardiac Care BACC; NCT02355457) Display omitted