Background The recent advent of subcutaneous implantable cardioverter defibrillators (S-ICDs) has provided investigators with a safe and effective new therapy in patients at risk of sudden cardiac death. At present, no data are available with regard to the longevity of these new devices. This study evaluated the longevity of the S-ICD system. Methods and Results All patients enrolled in the European Regulatory Trial were included in the analysis. During follow-up, time and causes of device replacement or explantation were assessed and categorized. Device longevity was estimated using Kaplan-Meier analysis. Fifty-five patients were followed for a median of 5.8 years. During follow-up, 26 (47%) patients underwent device replacement and 5 (9%) underwent device explantation. Median time to replacement was 5.0 years (Q1-Q3, 4.4-5.6 years). Replacement was caused by battery depletion in 25 patients (92%), of which 5 within 1.5 years because of premature battery depletion, and by infection in 1 patient (2%). Replacement for a transvenous ICD system was required in 4 patients (7%) because of ineffective defibrillation in 1 (0.003 per patient-year), need for resynchronization therapy in 2 (0.01 per patient-year), and for antibradycardia pacing in 1 (0.003 per patient-year). At 5 years follow-up, 71% of devices were still in service. Conclusions This study provides the first estimate of S-ICD system longevity since its introduction in clinical practice. Median longevity of the first generation S-ICD system was 5.0 years. The majority of devices were replaced because of battery depletion. Clinical Trial Registration URL: http://www.clinicaltrials.gov. Unique identifier: NCT01117792.