Prognosis of pandemic influenza A (H1N1) virus pneumonia is worse than community-acquired pneumonia (CAP), therefore it is important to know distinctive clinical features of both pneumonias. The aims of this study were to compare clinical features and prognosis of patients with pandemic influenza A (H1N1) pneumonia and CAP due to other agents. Demographic features, symptoms and findings of 20 pandemic influenza A (H1N1) pneumonia and 18 CAP patients hospitalized between October 1st and December 30th, 2009 were evaluated. One patient (5.0%) with pandemic Influenza A (H1N1) pneumonia and 55.6% of CAP patients were over 65 years (p= 0.001). Symptoms of fever, dyspnea, fatigue, muscle and joint pain, nausea, vomiting and headache were more frequent (p< 0.05), platelet count (p= 0.024) and PaO(2)/FiO(2) ratio (p= 0.006) were lower, number of thrombocytopenic patients (p= 0.024) and LDH levels (p= 0.016) were higher, duration of hospitalization was longer (p= 0.038) in patients with pandemic influenza A (H1N1) pneumonia. There was no difference in terms of radiological findings between two groups. None of the CAP patients were followed-up in the intensive care, whereas five pandemic influenza A (H1N1) pneumonia patients (25.0%) required intensive care and three of them died despite invasive mechanical ventilation. In conclusion, in the presence of fever, dyspnea with non-pulmonary symptoms and accompanying radiological alveolar opacities should be considered as pandemic influenza A (H1N1) pneumonia should be suspected in patients admitted with findings of pneumonia during influenza season. Admission to the intensive care unit and mechanical ventilation should be considered in patients with dyspnea and diffuse radiological findings.