OBJECTIVE: To identify differential clinical, laboratory, and echocardiographic characteristics in persons with diagnosed idiopathic and secondary pericarditis. METHODS: From January 1999 to December 2001, 84 patients with clinically and echocardiographically diagnosed pericarditis were identified in a heart clinic. These patients were analyzed according to age, sex, anthropometric measurements, body habitus, casual blood pressure (BP), signs and symptoms, morbid history, medicines and complications. The individuals were divided into 2 groups: group A comprised 61 patients with known causes of pericarditis and group B comprised 23 patients with idiopathic causes. The groups were compared with chi-square test. P<0.05 was considered statistically significant. RESULTS: The population of these 2 groups was similar in age, sex, anthropometric measures, body habitus, and casual BP. In group B (idiopathic), 23 (100%) cases were diagnosed between April and August versus 24 (39.4%) in the same period for group A (P<0.01). Twenty-three (100%) group B patients received anti-influenza vaccine versus none in group A. Breathlessness (P=0.02) and swelling (P=0.01) were more frequent in group A, but fatigue was more common in group B (P=0.01). For treatment, non-steroidal anti-inflammatory drugs (NSAID) were prescribed to 5 (8.2%) patients in group A and 19 (82.6%) in group B (P=0.01). CONCLUSION: In this series, patients labeled as having idiopathic pericarditis who had previously taken the influenza vaccine had seasonal distribution, a lower prevalence of previous disease, less exuberant signs and symptoms, and clinical regression with NSAID use.