Pericardial cysts are generally described as round radiodensities typically found at the right cardiophrenic angle in asymptomatic individuals. A review of all cases of pericardial cysts from the files of this Institute reveals that approximately one third of the cysts are found in other locations and that approximately one third of patients have symptoms of chest pain, dyspnea, or persistent cough. The radiographs of 41 patients show that in all but 6 of the cases the cyst is visualized as a round radiodensity touching both the hemidiaphragm and the anterior chest wall. Surprisingly, 15 of the 41 occurred on the left border of the heart. The six cysts significantly above the diaphragm were difficult to diagnosis radiologically and were usually mistaken for thymomas or pulmonary masses; two such cysts caused bronchial obstruction. In general, the possibility that a mass in either anterior cardiophrenic angle is a pericardial cyst should be strongly considered, even if the mass is on the left side and even if the patient is symptomatic.