We report our experience with implantable cardioverter defibrillator (ICD) implantation and follow-up in high-risk patients with congenital long QT syndrome (LQTS). Congenital LQTS is associated with significant risk of malignant ventricular arrhythmias and sudden cardiac death (SCD). ICD implant is recommended for prevention of SCD in this patient population, but there are few published data regarding the efficacy and side effects of such therapy. We report our experience with 12 patients who underwent ICD implant for high-risk LQTS at our center in the past 5 years with respect to implant complications, appropriate and inappropriate therapies, device follow-up, and the impact on lifestyle. During a follow-up of 34.7+/-16.6 months, appropriate therapies were noted in 5, inappropriate therapies in 4, and no therapies in 3 patients. Clusters of appropriate therapies were seen in 3 patients, 1 of whom subsequently died. Female sex and congenital deafness appear to be associated with a higher risk of appropriate therapies. One patient experienced two complications at implant that were successfully treated. ICD implantation in LQTS patients presenting with SCD or recurrent syncope despite beta-blocker therapy appears to be justified in preventing SCD risk. In asymptomatic siblings of SCD patients, the benefits of ICD implant are not clear from our data.