Background: H1N1 influenza A virus infections were first reported in April 2009 and spread rapidly, resulting in mortality worldwide. The aim of this study was to evaluate patients with H1N1 infection treated in the intensive care unit (ICU) in Bursa, Turkey. Methods: Demographic characteristics, clinical features, and outcome relating to H1N1 infection were retrospectively analysed in patients treated in the ICU. Results: Twenty-three cases of H1N1 infection were treated in the ICU. The mean age of patients was 37 years range: (17-82). Fifteen patients were female (65.2%). The mean Acute Physiology and Chronic Health Evaluation (APACHE) II score was 19 range: (5-39). The most common symptoms were dyspnea (73.9%), fever (69.6%), and cough (60.9%). Mechanical ventilation was required for all patients. Oseltamivir and antibiotics were administered to all patients. Six (26.1%) patients died. APACHE II scores were higher in the deceased 28.5 range: vs. 14 range: in survivors; p = 0.013). Conclusion: When compared to the literature, the demographic, epidemiological, and clinical characteristics were similar in the cases we encountered. The mortality rate was high despite the use of appropriate treatment. We believe that the high mortality is related to higher APACHE II scores. The H1N1 virus should be considered in community acquired pneumonia, especially in younger patients presenting with severe pneumonia.