ABSTRACT Background and Objectives: Hypertophic cardiomyopathy (HCM) is the most common genetic cardiac disease associated with sudden cardiac death (SCD). Immplantable cardioverter-defibrillators (ICDs) have proved effective in preventing SCD in patients with HCM. The efficacy of antitachycardia pacing (ATP) in patients with HCM has not been studied systematically. Subjects and Methods: From April 1996 to November 2010, 38 patients with HCM undergoing implantation of ICDs were enrolled. The indication of ICDs was for primary and secondary prevention in 13 and 25 patients, respectively. Among the patients with ICDs for secondary prevention, 13 patients presented with VF or SCD, while 12 patients presented with stable VTs. Eighteen Patients received ICDs programmed to deliver ATP for VT. Clinical characteristics, follow-up events and intracardiac electrograms were reviewed. Results: During a median follow-up period of 4.9짹3.3 years, a total of 207 episodes of ventricular tachycardia (VT) occurred in 12 patients, while ventricular fibrillation (VF) was recorded in only 1 episode. The cumulative incidence of VT and VF was 35.4짹8.3% and 4.5짹4.4% at 5 year, respectively. There was no significant difference in the cumulative incidence between primary and secondary indication (33.3짹13.6 % vs. 36.0짹10.5%, Log rank p=0.756). In patients where ATP was programmed on, ATP was attempted for 155 VT episodes in 6 patients, and 149 (96.1%; GEE-adjusted, 95.5%) of the VTs were successfully terminated by ATP alone. One VT was accelerated by ATP and terminated by ICD shock; 5 episodes were terminated spontaneously or by ICD shock. Conclusions: VT is the major mechanism of tachycardia in patients with HCM and SCD or in patients without previously documented VTs. An empirical programming of ICDs for ATP therapy could successfully terminate most VT episodes and decrease the number of unnecessary ICD shocks.