To assess the etiology and prognosis of a large pericardial effusion, we reviewed 25 consecutive patients who presented with a large pericardial effusion and underwent a drainage procedure. Large pericardial effusion was defined as: (1) an echo-free space greater than or equal to 10 mm anteriorly and posteriorly by M-mode echocardiography and (2) removal of greater than or equal to 350 ml of fluid at pericardial drainage. The etiologies of large pericardial effusion were: neoplastic (36%), idiopathic (32%), uremic (20%), postmyocardial infarction (8%), and acute rheumatic fever (4%). Of our patients, 44% presented with cardiac tamponade, while 25% of patients with idiopathic pericarditis had hemorrhage effusion and cardiac tamponade. At follow-up, 37 +/- 17 months after pericardial drainage, 68% had died from complications of their underlying disease. There were no deaths attributed to pericardial disease. While 88% of patients with idiopathic large pericardial effusion were alive at follow-up, none of the neoplastic large pericardial effusion patients survived longer than 5 months after initial pericardial drainage (p less than 0.001). Additionally, the survival of patients with uremic large pericardial effusion was better than patients with neoplastic large pericardial effusion (p less than 0.05). We conclude: (1) neoplastic, idiopathic, and uremic pericarditis are the most common causes of large pericardial effusion in men, (2) idiopathic pericarditis can be hemorrhagic and cause cardiac tamponade, and (3) the prognosis of large pericardial effusion is related to patients' underlying disease.