Severe community-acquired pneumonia (CAP) is an important cause of intensive care unit (ICU) admissions. Many different pneumonia scoring systems have been developed in order to assess the severity of pneumonia and to decide the ICU follow-up and treatment. But still debate is going on about their performances and also they have not been tested yet if they can predict ICU mortality in severe CAP patients requiring mechanical ventilation. The aim of this study is to evaluate the performances of pneumonia and ICU scores in predicting mortality in CAP patients requiring mechanical ventilation. A retrospective observational cohort study. The files of mechanically ventilated CAP patients were reviewed and demographic, clinic and laboratory characteristics were recorded. Scoring systems of pneumonia [revised American Thoracic Society (ATS) criteria, CURB-65, pneumonia severity index (PSI)] and ICU [Acute Physiology Assessment and Chronic Health Evaluation (APACHE) II, Sequential Organ Failure Assessment] were compared for mortality prediction. Thirty eight female and 63 male, a total of 101 severe CAP patients, with the mean age of 68 +/- 16 years, were included in the study. ICU mortality rate was assessed as 55%. Ninety percent of all patients met the revised ATS criteria and 92% of them met the PSI scoring system for ICU admissions. Although the CURB-65, PSI, revised ATS criteria were not found valuable to predict mortality, the increased APACHE II score was found to be related with increased mortality rate (for APACHE II > 20 odds ratio: 3, 95% CI: 1.2-7, p= 0.024). These results suggest that instead of the pneumonia scoring systems the APACHE II score can best predict the ICU mortality. So, more attention should be paid for severe CAP patients with APACHE II score > 20.