Cytomegalovirus is responsible for an opportunistic infection that can be life threatening in immunocompromised patients, while it is usually mild or completely asymptomatic in immunocompetent subjects. In the recent years, however, some cases of severe cytomegalovirus infection in immunocompetent patients have been reported, showing this to be a less rare occurrence than previously reported. We report the case of an 83-year-old man, admitted to our hospital for gastroenteritis, complicated by dehydration and severe prothrombin time prolongation due to oral anticoagulant therapy accumulation, who developed hospital-acquired pneumonia; neither of these illnesses responded to several lines of antibiotic therapy. All microbiologic tests were negative, except cytomegalovirus DNA test in blood, which showed high viral load. Antiviral therapy with ganciclovir was then started and a quick favourable response followed. A state of immunodeficiency was excluded, based on normal CD4 count and patient's clinical history. Different risk factors for severe cytomegalovirus disease in immunocompetent patients may exist, besides the ones already known, which could be responsible for severe cytomegalovirus disease in immunocompetent patients; thus, these patients should be tested for cytomegalovirus infection, if the clinical picture is compatible, to avoid delay in diagnosis and allow prompt start of specific therapy.