Background: Acute respiratory distress syndrome (ARDS) is a serious complication of sepsis, and sepsis-associated ARDS is associated with significant morbidity and mortality. To date, no study has directly examined the epidemiology of ARDS in severe sepsis from the earliest presentation to the health care system, the emergency department (ED). Methods: This was a single-center retrospective, observational cohort study of 778 adults with severe sepsis presenting to the ED. The primary outcome was the development of ARDS requiring mechanical ventilation during the first 5 hospital days. Acute respiratory distress syndrome was defined using the Berlin definition. We used multivariable logistic regression to identify risk factors associated independently with ARDS development. Results: The incidence of ARDS was 6.2% (48/778 patients) in the entire cohort. Acute respiratory distress syndrome development varied across the continuum of care: 0.9% of patients fulfilled criteria for ARDS in the ED, 1.4% admitted to the ward developed ARDS, and 8.9% admitted to the intensive care unit developed ARDS. Acute respiratory distress syndrome developed a median of 1 day after admission and was associated with a 4-fold higher risk of in-hospital mortality (14% vs. 60%, P < 0.001). Independent risk factors associated with increased risk of ARDS development included intermediate (2–3.9 mmol/L) (P = 0.04) and high (≥4) serum lactate levels (P = 0.008), Lung Injury Prediction score (P < 0.001), and microbiologically proven infection (P = 0.01). Conclusions: In patients presenting to the ED with severe sepsis, the rate of sepsis-associated ARDS development varied across the continuum of care. Acute respiratory distress syndrome developed rapidly and was associated with significant mortality. Elevated serum lactate levels in the ED and a recently validated clinical prediction score were independently associated with the development of ARDS in severe sepsis.