Three cases of adenocarcinoma of the lung manifesting as acute pericardial effusion with tamponade are presented and the medical literature concerning this unusual manifestation of extracardiac malignancy is reviewed. We have found 22 cases of carcinoma and 4 cases of sarcoma. Of the carcinomas, 14 of 19 (74%) with known primary are pulmonary and 13 of 18 (72%) with tissue diagnosis are adenocarcinomas. Daignosis was made by cytologic examination of pericardial fluid in 14 of 16 cases (87%) in which it was performed. The lymphatic drainage of the heart renders some anatomical explanations for the prevalence of carcinoma of the lung as the cause of cardiac tamponade and the discrepancy of finding tumor cells in the pericardial fluid but not in the pericardium. Patients treated with pericardiectomy with or without ancillary radio- or chemotherapy survived longer than those treated with periocardiocentesis or radio- or chemotherapy alone.