Objective: Unlike seasonal influenza, seen in previous years, the strain identified in the 2009 influenza-A pandemic involved high mortality. In this study, prognostic factors and general characteristics of pneumonia cases developed in Turkey during the H1N1 pandemic between October 2009 and January 2010 were analyzed. Study Design: Multicenter retrospective study. Material and Methods: This multicentric retrospective study was conducted between August and October 2010 and patients' data were collected by means of standard forms. Results: The study included 264 pneumonia cases, collected from 14 different centers. Mean age was 47.5±18.6 years. Nineteen patients (7.2%) were pregnant or had a new birth and comorbid diseases were detected in 52.3% of all patients. On admission, 35 (13.8%) cases had altered mental status. Overall, 32.6% were treated in intensive care units (ICU) and invasive/non-invasive mechanical ventilation was performed in 29.7%. The mean duration of ICU stay was 2.9±6.2 and total hospital stay was 12.0±9.4 days. Mortality rate was 16.8% (43-cases). The length of ICU treatment, total hospital stay, and mortality were significantly higher in H1N1-confirmed patients. Mortality was significantly higher in patients with dyspnea, cyanosis, and those who had altered mental status on admission. Patients who died had significantly higher rate of peripheral blood neutrophils, lower platelet counts, higher BUN, and lower SaO2 levels. Conclusion: This study showed that pneumonia developed during H1N1 pandemic in our country had resulted in a high mortality. Mortality was especially high among patients with cyanosis, altered mental state and those with lower SaO2. © Trakya University Faculty of Medicine.