The Role of Clinical Parameters in the Prognosis of Severe Community-acquired Pneumonia Patients with severe community-acquired pneumonia (CAP) who require intensive care unit (ICU) treatment have been reported to have a mortality rate of up to 70%. The aim of the present study was to investigate the effect of some clinical and laboratory indices on the outcome of CAP. A total of 48 patients with severe CAP (24 male, 24 female, mean age 64±18 years) admitted in our respiratory ICU were enrolled in the study. The overall mortality rate was found as 52.1%. Twenty-three patients (47.3%) were on antibiotic treatment before ICU admission and comorbid diseases were present in 38 of 48 patients (79.2%). Pleural effusion was detected in chest X-ray of 17 patients (35.4%) and radiological multilobar involvement of pneumonia was found at 39 of 48 patients (81.2%). The responsible microorganism was isolated in 17 patients (35.4%) and the leading pathogens were found to be Streptococcus pneumoniae and Staphylococcus aureus. The mean APACHE II score was 16.06±5 in our study population. The mortality rates in patients with APACHE II score more or less than 16 were found as 71.4% and 37.0%, respectively (c2=5.60, p=0.018) and in patients whose length of total hospital stay was less or more than 10 days were found as %78.9 and %34.5, respectively (c2=9.09, p=0.003). In patients who required mechanical ventilatory support the mortality rate was %87.5, whereas in patients who did not it was %34.8 (c2=12.06, p=0.001). No other significant differences were found between the outcome of pneumonia and all other investigated parameters.