A 63-year-old woman had persistent bloody pericardial effusion. Tuberculous pericarditis was initially suspected, but empirical antituberculosis therapy was futile. FDG PET/CT study revealed abnormal FDG activity in multiple parts of the pericardium, especially along with aorta and main pulmonary artery, and in the left atrium. However, there was no abnormal activity in other parts of the body. Histopathologic examination revealed primary pericardial angiosarcoma.