Background: The purpose of this study was to investigate prognosis of patients with idiopathic pericardial effusion (PE) and identify prognostic factors in Korea that is tuberculosis (TBc)-endemic area. Methods: Of 672 patients with PE who underwent pericardiocentesis or pericardial window operation between January 1997 and December 2009, 63 (9.4%) (age: 60짹15 years, 43 females) were finally diagnosed as idiopathic PE. Initial clinical and laboratory findings were evaluated, and clinical events defined as death, pericardiectomy, and repeated PE drainage were observed for a median of 30 months. Results: Of 63 patients, 9 were asymptomatic. Non-steroidal anti-inflammatory drugs, colcichine, and empirical anti-TBc medications were used in 5, 1 and 14 patients, respectively. During follow-up period, no mortality was observed. Two patients underwent pericardiectomy after 2.5 and 4.5 months after the day of initial drainage procedure due to development of constrictive pericarditis, and another 2 underwent repeated pericardial window operation. The 4 patients (6.3%) with clinical events showed higher prevalence of hemodynamic significance on the initial echocardiography (40% vs. 3.6%, p=0.031) and lower platelet count (166800짹54085 vs. 284844짹114527/mm3, p=0.027) than others without clinical events. There was no difference in clinical events between the patients treated with and without anti-TBc medication (7.1% vs. 6.1%, p=0.89). By multivariate Cox proportional hazard model, only independent predictor for clinical events was hemodynamic significance on the initial echocardiography (hazard ratio: 16.675, 95% confidence interval: 1.109 to 250.684). Event-free survival rates were significantly higher in 5 patients with the initial hemodynamic significance than in 56 patients without (Figure, p<0.001). Conclusion: Idiopathic PE seems to be a benign disease, and hemodynamic significance on the initial echocardiography is a major prognostic factor. Empirical anti-TBc medications may not be justified for these patients in Korea.