Background: Acute respiratory distress syndrome (ARDS) is a clinical syndrome of severe dyspnoea of rapid onset, hypoxemia, and diffuse pulmonary infiltrates leading to respiratory failure in the absence of cardiac failure. We did the study to asses various aetiologies of ARDS, to determine the correlation between the diagnostic criteria, mortality predictors, need of mechanical ventilation and the outcome of patients. This was an observational, prospective study in medical intensive care unit (MICU) of a tertiary care hospital, over a period of 15 months. Methods and Material: This study encompassed 116 patients of ARDS admitted to an MICU at a tertiary care centre in Mumbai. We included all consecutive patients with ARDS in this study. We excluded patients with known ischemic heart diseases, valvular heart diseases or in congestive cardiac failure, chronic kidney diseases with fluid overload states and age below 18 years. Results: Males comprised almost 70% (81) of the study population and the presentation was more common in younger age group with total mortality of 57.8% (67 out of 116). Factors attributable for ARDS were malaria in 31 patients (26.72%), pneumonia in 23 (19.82%), sepsis in 20 (17.2%), dengue in 15 (12.96%), undiagnosed fever in 13 (11.1%), leptospirosis in 7 (6.03%), pancreatitis in 3 (2.58%), H1N1 infection in 2 (1.72%), urinary tract infection (UTI) in 1 (0.86%) and UTI with pyelonephritis and Dengue in 1 (0.86 %) patients. Tropical diseases in present study constituted 66 (56.89%) cases of which 31 (47%) died. This difference was statistically found to be significant. Mean PaO2/FiO2 was 178.32 amongst discharged and 127.69 amongst those who expired. Sixty patients had severe LIS, out of which 45 (75%) patients expired, as compared to 56 patients with moderate LIS out of which 22 (39.3%) expired. Conclusion: Tropical diseases like malaria, dengue, and leptospirosis were the main factors responsible for ARDS. LIS, Modified LIS and PaO2/FiO2 ratio predicted outcome as well as need for mechanical ventilation. Renal failure, metabolic acidosis appeared to be good predictors of mortality.