Background: The implantable cardioverter defibrillator (ICD) is used to treat life-threatening ventricular arrhythmias and to prevent sudden cardiac death. Nowadays, ICD implantation for the purpose of primary prevention has been increasing. However, little is known about the difference of clinical characteristics, and outcomes between primary prevention and secondary prevention in patients with ICD implantation in Korea. Methods: We analyzed retrospectively 124 patients (55.8짹16.6 years old, 95 males) who underwent ICD implantation at Chonnam National University Hospital from January 1999 to June 2011. We checked basal clinical characteristics, laboratory findings and indication of ICD implantation. Median follow-up duration was 3.5짹2.7 years. Primary prevention was defined as no history of sudden cardiac death nor life threatening arrhythmia. Patients were divided into primary prevention group (n=12) and secondary prevention group (n=111). Results: ICD was implanted for the purpose of primary prevention in 7 ischemic cardiomyopathy patients, and 5 dilated cardiomyopathy patients and for the purpose of secondary prevention in patients with idiopathic ventricular tachycardia (17 patients, 15.3%), ischemic cardiomyopathy (23 patients, 20.7%), idiopathic ventricular fibrillation (13 patients, 11.7%), Brugada syndrome (24 patients, 21.6%), dilated cardiomyopathy (19 patients, 17.1%), long QT syndrome (5 patients, 4.5%), arrhythmogenic right ventricular dysplasia (5 patient, 4.5%). Baseline demographic and laboratory finding were not different between the 2 groups except for higher prevalence of diabetes mellitus (41.7% vs. 11.8%, p=0.016) in primary prevention group. During median 3.5 years of follow-up, 9 patients (9.0%) were died. Primary prevention group did not receive ICD shock. However, secondary prevention group received significantly higher appropriate shock than inappropriate shock (27.3% vs. 8.2%, p=0.044). Mortality rate of primary prevention group was not different from secondary prevention group even after covariate adjustment. Conclusions: ICD provided similar survival benefits to both primary and secondary prevention group. Also, ICD exerted significantly higher appropriate shock than inappropriate shock.