Malignant primary tumors of the pericardium are rare. The authors present two male patients, aged 44 and 67 years, not exposed to asbestos, who died from pericardial mesothelioma. Repeated evacuation of fluid from the pericardium due to cardiac tamponade failed to reveal the cause of pericarditis. In one case, the diagnosis was made on surgical exploration, and in the other, at autopsy. A significant difference between benign and malignant pericardial effusion was observed. In cases of pericardial mesothelioma, symptoms of epicardial involvement cannot be attributed solely to the hindered inflow and cardiac tamponade, but also to congestive heart failure due to myocardial infiltration. In one patient, temporary improvement was achieved, first by pronisone therapy and then by radiotherapy.