Rationale: Although proposed as a clinical prompt to sepsis based on predictive validity for mortality, the Quick Sepsis-related Organ Failure Assessment (qSOFA) score is often used as a screening tool, which requires high sensitivity.Objectives: To assess the predictive accuracy of qSOFA for mortality in Brazil, focusing on sensitivity.Methods: We prospectively collected data from two cohorts of emergency department and ward patients. Cohort 1 included patients with suspected infection but without organ dysfunction or sepsis (22 hospitals: 3 public and 19 private). Cohort 2 included patients with sepsis (54 hospitals: 24 public and 28 private). The primary outcome was in-hospital mortality. The predictive accuracy of qSOFA was examined considering only the worst values before the suspicion of infection or sepsis.Measurements and Main Results: Cohort 1 contained 5,460 patients (mortality rate, 14.0%; 95% confidence interval [CI], 13.1-15.0), among whom 78.3% had a qSOFA score less than or equal to 1 (mortality rate, 8.3%; 95% CI, 7.5-9.1). The sensitivity of a qSOFA score greater than or equal to 2 for predicting mortality was 53.9% and the 95% CI was 50.3 to 57.5. The sensitivity was higher for a qSOFA greater than or equal to 1 (84.9%; 95% CI, 82.1-87.3), a qSOFA score greater than or equal to 1 or lactate greater than 2 mmol/L (91.3%; 95% CI, 89.0-93.2), and systemic inflammatory response syndrome plus organ dysfunction (68.7%; 95% CI, 65.2-71.9). Cohort 2 contained 4,711 patients, among whom 62.3% had a qSOFA score less than or equal to 1 (mortality rate, 17.3%; 95% CI, 15.9-18.7), whereas in public hospitals the mortality rate was 39.3% (95% CI, 35.5-43.3).Conclusions: A qSOFA score greater than or equal to 2 has low sensitivity for predicting death in patients with suspected infection in a developing country. Using a qSOFA score greater than or equal to 2 as a screening tool for sepsis may miss patients who ultimately die. Using a qSOFA score greater than or equal to 1 or adding lactate to a qSOFA score greater than or equal to 1 may improve sensitivity.