Objective: to prove that pericardial effusion could be a sign of serious diseases. Design: 5 years prospective study. Setting: Medical and cardiac departments of EL Fateh children hospital in Benghazi/ Libya. Method All cases referred to cardiac clinic in this hospital with cardiomegally in the chest x -ray, and whom Echocardiogram showed pericardial effusion in the period between 1st January 2003 to1st December 2007 were included in the study, . Results 87 patients had pericardial effusion, 56 (64.36 % ) were males, and 31 (35.64% ) were females, so male: female ratio is 1.8:1.causes: 33 (37.93%) was due to viral infection, 11 (12.65%) with congenital heart diseases, 8 (9.2%) rheumatoid arthritis, 7 (8.05%) malignancy, 7 (8.05%) postpericardiotomy, 6 (6.89%) renal diseases, 3 (3.44%) Bacterial infection., 3 (3.44%) Rheumatic fever, 2 (2.3%) skin lesions, 2 (2.3%) Tuberculosis, 2 (2.3%) infective endocarditis, 1 (1.15%) Systemic lupus erythromatosis, 1 (1.15%) Kawasaki disease, 1 (1.15%) diagnosed intrauterine.Treatment : Surgical drainage was performed on 3 (3.45%) , 5 ( 5.75% ) pericardio_ centesis, 21 ( 24.14% ) treated with small dose of diuretics. 19 ( 21.85% ) treated by steroid ± aspirin, 5 (5.75% ) by intravenous antibiotics, 7 ( 8.05%) treatment of malignancy, 6 ( 6.89%) treatment of renal disease, the rest 21 (24.12%) were small amount and resolve spontaneous without treatment. Conclusions : Echocardiography is a good method for diagnosis and follow up of pericardial effusion and cardiac tamponade. the pericardial effusion could be a sign of serious systemic diseases.