BACKGROUND–: The implantable cardioverter-defibrillator (ICD) is effective for preventing sudden death in patients with hypertrophic cardiomyopathy (HCM). However, data on performance and complications of implanted ICDs over particularly long time periods to inform clinical practice is presently incomplete. METHODS–: The study cohort comprises 217 consecutive HCM patients with primary prevention ICDs implanted prior to 2008 and followed for ≥10 years (mean 12 ± 4; range to 31). RESULTS–: Patients were 38 ± 17 years at implant and 45 (21%) experienced appropriate interventions terminating VT/VF. The majority of ICD discharges occurred ≥ 5 years after implant (29 patients; 64%), including ≥10 years in 16 patients (36%). Initial device therapy increased in frequency from 2.3% of patients at <1 year to 8.5% of patients at ≥ 10 years post implant (p=0.005). Inappropriate ICD shocks in 39 patients occurred most commonly <5 years after implant (54%) and decreased in frequency with increasing time from implant (from 9.7% of patients at <5-years to 3.8% at ≥10years, p=0.02). Other major device complications including infection and/or lead fractures and dislodgement occurred in 27 patients (12%), but did not increase in frequency over follow-up (p=0.47). There were no arrhythmic sudden death events among the 217 ICD patients. CONCLUSIONS–: In HCM, primary prevention ICD therapies increase progressively over time after implant, including a substantial proportion with prolonged periods of device dormancy, including two-thirds of patients ≥ 5-years and for ≥ 10 years in one-third. Frequency of inappropriate shocks decreased over follow-up, likely reflecting changes in device programming, while occurrence of device complications such as lead fractures/infection did not increase during follow-up.