The standard of care for patients with acute respiratory distress syndrome (ARDS) has been developed based on studies that usually excluded patients with major comorbidities. To describe treatments and outcomes according to comorbidities in patients with ARDS admitted to 19 ICUs (1997-2014). Patients were grouped based on comorbidities. Determinants of day-28 mortality were identified by multivariable Cox analysis stratified on center. Among 4953 ARDS patients, 2545 (51.4%) had major comorbidities; the proportion with major comorbidities increased after 2008. Hematological malignancy was associated with severe ARDS and rescue therapies for refractory hypoxemia. COPD, HIV infection, and hematological malignancy were associated with a lower likelihood of invasive mechanical ventilation on the admission day. Admission-day SOFA score was higher in patients with major comorbidities, who more often received vasopressors, dialysis, or treatment-limitation decisions. Day-28 mortality was 33.7% overall, 27.2% in patients without major comorbidities, and 31.1% (COPD) to 56% (hematological malignancy) in patients with major comorbidities. By multivariable analysis, mortality was lower in patients with COPD and higher in those with chronic heart failure, solid tumors, or hematological malignancies. Mortality was independently associated with PaO2/FiO2 and PaCO2 on day 1, ARDS of pulmonary origin, worse SOFA score, and ICU-acquired events. Half the patients with ARDS had major comorbidities, which were associated with severe ARDS, multiple organ dysfunction, and day-28 mortality. These findings do not support the exclusion of ARDS patients with severe comorbidities from randomized clinical trials. Trials in ARDS patients with whatever comorbidities are warranted.