IMPORTANCE: An international task force recently redefined the concept of sepsis. This task force recommended the use of the quick Sequential Organ Failure Assessment (qSOFA) score instead of systemic inflammatory response syndrome (SIRS) criteria to identify patients at high risk of mortality. However, these new criteria have not been prospectively validated in some settings, and their added value in the emergency department remains unknown. OBJ ECTIVE: To prospectively validate qSOFA as a mortality predictor and compare the performances of the new sepsis criteria to the previous ones. DESIGN, SETTINGS, AND PARTICIPANTS: International prospective cohort study, conducted in France, Spain, Belgium, and Switzerland between May and June 2016. In the 30 participating emergency departments, for a 4-week period, consecutive patients who visited the emergency departments with suspected infection were included. All variables from previous and new definitions of sepsis were collected. Patients were followed up until hospital discharge or death. EXPOSURES: Measurement of qSOFA, SOFA, and SIRS. MAIN OUTCOMES AND MEASURES: In-hospital mortality. RESULTS: Of 1088 patients screened, 879 were included in the analysis. Median age was 67 years (interquartile range, 47-81 years), 414 (47%) were women, and 379 (43%) had respiratory tract infection. Overall in-hospital mortality was 8%: 3% for patients with a qSOFA score lower than 2 vs 24% for those with qSOFA score of 2 or higher (absolute difference, 21%; 95% CI, 15%-26%). The qSOFA performed better than both SIRS and severe sepsis in predicting in-hospital mortality, with an area under the receiver operating curve (AUROC) of 0.80 (95% CI, 0.74-0.85) vs 0.65 (95% CI, 0.59-0.70) for both SIRS and severe sepsis (P < .001; incremental AUROC, 0.15; 95% CI, 0.09-0.22). The hazard ratio of qSOFA score for death was 6.2 (95% CI, 3.8-10.3) vs 3.5 (95% CI, 2.2-5.5) for severe sepsis. CONCLUSIONS AND RELEVANCE: Among patients presenting to the emergency department with suspected ...