Objective: Cytomegalovirus (CMV) infections in immunocompetent ICU patients have been associated with poor outcomes. We determined the distribution of cytomegalovirus coinfection among patients admitted in the ICU1 of Evangelismos Hospital of Athens with or diagnosed with pandemic influenza A (H1N1) respiratory infection. Patients:We examined retrospectively 33 ICU consequently patients with community or hospital-acquired pulmonary infection. Investigation of viral-viral coinfection rate was determined at the first 48 h after ICU admission.Results: A total of 13 patients that received a diagnosis of influenza A (H1N1) had their diagnosis confirmed by influenza A rapid antigen testing and/or by influenza A (H1N1) polymerase chain reaction (PCR). Only three out of the 13 H1N1 positive patients were cytomegalovirus bronchoalveolar lavage (BAL)-PCR positive and 10 were negative. Additionally 2 out of the 20 H1N1 negative patients were CMV-BAL-PCR positive. Conclusion:We did not find significant CMV distribution in our H1N1 positive patients at least at the early 4-5 days period after H1N1 infection. However, the study is interesting because patients with a combination of H1N1 and CMV infections have been described only rarely. The scarce presence of CMV in H1N1 patients may suggest that endogenous reactivation of CMV infection within the lungs does occur and that these patients may profit from antiviral therapy. The interplay between host and viruses is very complex and therefore the triggering for the CMV disease activation following H1N1 pneumonia is possible to require more than the absolute presents of the H1N1 virus especially in the ICU patients.