AimsThe clinical effectiveness of primary prevention implantable cardioverter defibrillator (ICD) therapy is under debate.The EUropean Comparative Effectiveness Research to Assess the Use of Primary ProphylacTic Implantable Cardioverter Defi-brillators (EU-CERT-ICD) aims to assess its current clinical value.Methods and resultsThe EU-CERT-ICD is a prospective investigator-initiated non-randomized, controlled, multicentre obser-vational cohort study performed in 44 centres across 15 European Union countries. We will recruit 2250 patients with ischae-mic or dilated cardiomyopathy and a guideline indication for primary prophylactic ICD implantation. This sample will include1500 patients at theirfirst ICD implantation and 750 patients who did not receive a primary prevention ICD despite having anindication for it (non-randomized control group). The primary endpoint is all-cause mortality; the co-primary endpoint in ICDpatients is time tofirst appropriate shock. Secondary endpoints include sudden cardiac death,first inappropriate shock, anyICD shock, arrhythmogenic syncope, revision procedures, quality of life, and cost-effectiveness. At baseline (and prior toICD implantation if applicable), all patients undergo 12-lead electrocardiogram (ECG) and Holter ECG analysis using multipleadvanced methods for risk stratification as well as detailed documentation of clinical characteristics and laboratory values. Ge-netic biobanking is also organized. As of August 2018, baseline data of 2265 patients are complete. All subjects will be followedfor up to 4.5 years.ConclusionsThe EU-CERT-ICD study will provide a necessary update about clinical effectiveness of primary prophylactic ICDimplantation.