OBJECTIVES: Implantable cardioverter defibrillator (ICD) is considered a lifelong therapy for the prevention of sudden cardiac death. However, it is still unresolved if patients who never experienced an appropriate ICD intervention during first generator longevity really need to undergo device replacement. METHODS: In a single-center prospective observational cohort study we examined the time-dependence of first appropriate ICD therapy for ventricular arrhythmias in patients who underwent ICD implantation for primary prevention. Primary prevention ICD patients were enrolled at the time of their first implantation and were evaluated thereafter for the first occurrence of appropriate ICD therapy for ventricular arrhythmias. RESULTS: Of 623 ICD recipients, 126 (20,2%) had appropriate ICD therapy. Incidence of first appropriate ICD therapy was 8.2% in the first year post-implant, increased to 13.7% in year 2, while in year 5 it was 28.3% (fig 1). Notably 39 patients received their first appropriate therapy after device replacement. No predictive factors for lower need of ICD therapy could be identified in patients without prior appropriate ICD intervention. CONCLUSIONS: In a primary prevention population the risk of first appropriate ICD therapy persists over long lifetime and necessitates continuing device therapy irrespective of shock-free intervals.