The pericardium is involved in a large number of systemic disorders, and acute pericarditis may be due to several causes. The diagnosis is based on clinical criteria, and laboratory testing is not routinely recommended. Deciding on the extent of the diagnostic evaluation requires good clinical judgement based on a careful evaluation of the risk-benefit ratio, and knowledge of basic epidemiological data for the development of a rational management program. In clinical practice a probabilistic approach seems reasonable: in Western countries most cases are idiopathic or viral with a brief and benign course and an excellent response to non-steroidal anti-inflammatory drugs, thus an extensive diagnostic evaluation is not routinely necessary. On the contrary, in developing countries specific pericarditis such as tuberculous pericarditis is quite common and should be ruled out. A clinical triage is feasible on a clinical basis. Patients with pericarditis can be safely managed on an outpatient basis without a thorough diagnostic evaluation unless the patient has high risk features such as temperature >38 degrees C, a subacute onset, immunodepression, a history of recent trauma, oral anticoagulant therapy, myopericarditis, a large pericardial effusion, and cardiac tamponade. The reported diagnostic yield of extensive laboratory evaluation and pericardiocentesis is low in the absence of cardiac tamponade or suspected purulent, tuberculous, and neoplastic pericarditis. Invasive procedures should be limited mainly to patients in whom therapeutic intervention is necessary.