Background Sudden cardiac death (SCD) is the most devastating complication of hypertrophic cardiomyopathy (HCM), but this can be prevented by an implantable cardioverter-defibrillator (ICD). The aim of this study is to evaluate HCM patients with ICDs for primary or secondary prevention of SCD. Methods The study population consisted of all HCM patients with an ICD in 2 tertiary referral clinics. End points during follow-up were total and cardiac mortality, appropriate and inappropriate ICD intervention, and device-related complications. Cox-regression analysis was performed to identify predictors of outcome. Results ICDs were implanted in 134 patients with HCM (mean age 44 ± 17 years, 34% women, 4.2 ± 4.8 years follow-up). Annualized cardiac mortality rate was 3.4% per year and associated with New York Heart Association class III or IV (HR 5.2 2.0-14, P = .002) and cardiac resynchronization therapy (HR 6.3 2.1-20, P = .02). Appropriate ICD interventions occurred in 38 patients (6.8%/year) and was associated with implantation for secondary prevention of SCD (HR 4.0 1.8-9.1, P = .001) and male gender (HR 3.3 1.2-9.0, P = .02). Inappropriate ICD intervention occurred in 21 patients (3.7%/year) and in 20 patients device related complications were documented (3.6%/year). Conclusion ICDs successfully abort life-threatening arrhythmias in HCM patients at increased risk of SCD with an annualized intervention rate of 6.8% per year. End-stage heart failure is the main cause of mortality in these patients. The annualized rate of inappropriate ICD intervention was 3.7% per year, whereas device-related complications occurred 3.6% per year.