Aim: Acute respiratory distress syndrome (ARDS) is an acute hypoxemic respiratory failure refractory to oxygen therapy. The incidence of ARDS is not high, but its management is very difficult for the intensivist and the mortality rate is high. In this study, the general characteristics of patients with ARDS in a medical intensive care unit (ICU) in a university hospital were evaluated. The mortality rate in these patients was determined and factors related to mortality were assessed. Material and Methods: Patients who had ARDS upon admission or developed ARDS after admission between April 2007 to August 2010 in our medical ICU were included in the study. The prospective data of ARDS patients were studied retrospectively. Demographic characteristics, reasons for ARDS, treatment modalities, mortality rate and factors determining mortality were evaluated. Results: One thousand one hundred and twenty-five (1125) patients were admitted to our medical ICU during the study period. Ninety (8%) patients had ARDS upon admission or developed ARDS after admission in this period. These ARDS patients were accepted as the study group. The median age was 46 [30-60] and 61% of patients were male. Upon admission, the APACHE II and Glasgow coma scores were 23 [17-28] and 15 [11-15], respectively. The most common underlying disease was hematological malignancy (57%). Sixty-two percent (62%) of patients were immunocompromised. The most common etiologies of ARDS were pneumonia (58%) and sepsis (21%). The ratio of partial oxygen pressure to inspired oxygen fraction (PaO2/FiO2) was 113 [76-166] mmHg. Nineteen percent (19%) of ARDS patients received non-invasive mechanical ventilation (NIMV), 30% received invasive mechanical ventilation (IMV), and 48% received both NIMV and IMV. ICU and hospital stay were 8 [4-14] and 22 [12-38] days, respectively. ICU and hospital mortality were 66% (59) and 70% (63), respectively. Performing NIMV and admission from the emergency room (ER) were found to be independent risk factors associated with lower mortality, whereas the development of immunosuppression and sepsis in the ICU were independent risk factors associated with higher mortality. Conclusion: The ICU mortality rate was 66% in our ARDS patients. We also found that immunosuppression and sepsis that developed in the ICU increased the mortality rate, while performing NIMV and admission from the ER reduced the mortality rate in our ARDS patients.