Aims: Prevention of sudden cardiac death by means of the implantable cardioverter/defibrillator (ICD) is considered to be a lifelong therapy. However, it is still unresolved if patients who never experienced an appropriate ICD intervention during generator longevity really need to undergo device replacement., Methods and Results: The INSURE trial was a multicentre prospective observational cohort study that enrolled patients at the time of their first ICD replacement. Patients with and without previous appropriate ICD therapy were enrolled prospectively and were evaluated every 3-6 months after ICD replacement. Primary endpoint of the study was the first occurrence of appropriate ICD therapy after device replacement. Five hundred and ten patients (83% males, mean age 65 ± 10 years, mean ejection fraction 39 ± 16%) were enrolled between 2002 and 2007 in the study after an average lifespan of their first ICD generator of 62 ± 18 months. Three years after elective ICD replacement, the rates of appropriate ICD therapies in patients with (n = 245) and without (n = 265) former appropriate ICD intervention were 48.1 and 21.4% (adjusted hazard ratio 3.08, CI: 2.15-4.39, P < 0.001). Notably, no predictive factors for lower need of ICD therapy could be identified in patients without prior appropriate ICD intervention., Conclusions: In this study, a significant number of ICD-indicated patients without the need for therapy by their first device received appropriate ICD intervention after generator replacement. There were no predictors for lower need of ICD therapy. Hence, ICD replacement appears still necessary in patients without prior ICD interventions.