In conclusion, significant epidemiological changes and an increased severity of influenza A (H1N1) 2009 pneumonia were found in the first post-pandemic influenza season. Physicians dealing with patients with pneumonia in the upcoming influenza seasons should carefully consider influenza A (H1N1) 2009 as a possible causative agent when ordering microbiological tests and selecting treatment. Early diagnosis and antiviral therapy of influenza A (H1N1) 2009 pneumonia would help to improve patient outcomes.