Background: Inappropriate shocks of implantable cardioverter defibrillator (ICD) have a major impact on morbidity and quality of life in ICD patients. However, little is known about the ICD therapies in Korean patients. The present study aimed to analyze the inappropriate shocks in patients with ICD in single tertiary center. Methods: Thirty-nine ICD implanted patients (32 male, mean age: 48 짹 13 years) between 1998 and 2005 were analyzed, retrospectively. The indications of ICD implantation were aborted sudden cardiac death in 17 patients, syncope or ventricular tachycardia in 7 patients, Brugada syndrome in 11 patients, and ventricular tachycardia with ischemic cardiomyopathy in 4 patients. Incidence, causes, and time of inappropriate shocks were analyzed during a mean follow-up period of 37 짹 28 months. Results: There were total 76 ICD shocks in 13 patients (33.3%). Forty-one (54%) ICD shocks in 8 patients were appropriate and 35 (46%) shocks in 10 patients were inappropriate. Time to first inappropriate shocks was 20 짹 20 months. Inappropriate shocks were caused by lead complications in 16 (45.7%), atrial fibrillation or flutter in 8 (22.8%), sinus tachycardia in 7 (20%), T wave oversensing in 3 (8.5%), and noise oversensing in 1 (2.8%). Specific causes and treatments are shown in table. Conclusions: The rate of inappropriate shocks in patients with ICD is as high as 46% and the majority of which is caused by atrial fluttuer/fibrillation and lead complications. Future studies to evaluate clinical predictor and preventative strategies of inappropriate shocks are warranted.