Background: Leads in and on the heart of the transvenous implantable cardioverter defibrillator (ICD) form the Achilles' heel of this system due to potential for peri- and postimplant complications. The S-ICD is a newer generation of the ICD that does not require leads on the heart or in the vasculature. We present the rationale and study design of the Evaluation oF FactORs ImpacTing CLinical Outcome and Cost EffectiveneSS of the S-ICD (EFFORTLESS S-ICD) Registry which was designed to evaluate the long-term performance of the S-ICD including patient quality of life and long-term resource utilization. Methods: The Registry is an observational, nonrandomized, standard of care evaluation to be conducted at approximately 50 investigational centers in Europe and New Zealand where the S-ICD is approved for use and distribution. Clinical Registry endpoints include perioperative (30 days postimplant) complication-free rate, 360-day complication-free rate, and percentage of inappropriate shocks for atrial fibrillation and supraventricular ventricular tachyarrhythmia. Other endpoints include patient-reported outcomes (e.g., quality of life) and hospital personnel implant and follow-up experience with the S-ICD system. Conclusions: Results from EFFORTLESS will build on and expand the initial published experience with the S-ICD, which demonstrated that the device successfully and consistently detects and treats episodes of sustained ventricular tachyarrhythmias. The Registry will also evaluate the patients' perspective of how it is to live with an S-ICD as compared to a contemporary transvenous system and track the experience of implanting physicians and personnel performing patient follow-up with a completely subcutaneous system. (PACE 2012; 1-6).