Primary malignant mesothelioma of the pericardium is a very rare and highly lethal neoplasm. Diagnosis is a difficult problem and most of the cases reported in the literature were diagnosed at postmortem. We report a caseof primary malignant mesothelioma of the pericardium in a 22 year-old man. CT and MR imaging both showed diffuse irregular pericardial thickening, soft tissue density with cystic lesion, nodular bulging into the myocardium, permeative growth of the tumor, and encasement of the heart and two great vessels.