To assess the etiology and clinical course of moderate and severe pericardial effusions, we reviewed 118 consecutive patients seen in the cardiology department of the Kyunghee Medical Center from January, 1984 to July, 1988. 1) The common etiologies of pericardial effusions were tuberculosis(25.4%), malignancy(18.8%), uremia(16.2%), heart failure(14.4%), idiopathic(7.7%) and collagen vascular disease(5.1%). The lung cacer(77.2%) and breast cancer(9.1%) comprised most of the etiology of malignant pericardial effusion. The adenocarcinoma was the most common histologic entity of lung cancer. 2) Collapses of right atrium, right ventricle or both were seen in 17 case(14.4%), and the causes of collapses were malignancy(35.5%), idiopathic(11.8%) and uremia(11.8%). 3) The causes of constrictive pericarditis were : tuberculosis(42.9%), idiopathic(28.6%), malignancy(14.3%) and uremia(14.3%). 4) The percentages of improved cases were determined in 55 patients by echocardiography twice, 30th day after treatment and the last follow up day. It revealed 84%/96% in tuberculosis, 85.7%/0% in malignancy, 66.7%/83.3% in uremia, 83.3%/83.3% in heart failure, 100%/100% in both myxedema and myocardial infarction, and 33.3%/33.3% in collagen vascular disease at both follow up day. We conclude that the most common etiology of the pericardial effusions is still tuberculosis in Korea and the most common etiology of cardiac tamponade is malignancy, even though the suspected patients without echocardiography have been excluded can be a limitation of this study. The pericardial effusions by tuberculosis, uremia or heart failure responded well to the adequate treatment and response in malignancy or collagen vascular disease was not good.