Purpose of the study: Transvenous ICD therapy faces relevant limitations and contraindications in patients with congenital heart disease (CHD). The recently introduced entirely subcutaneous implantable cardioverter-defibrillator (S-ICD) offers a relevant alternative, as it does not need vascular access or thoracotomy. Methods used: S-ICD system was implanted in a heterogeneous group of 10 patients with structural CHD (age 8.9–62.0 y, height 73.0–208.0 cm, weight 34.0–130.0 kg). The majority presented with challenging hemodynamic and anatomical features such as univentricular anatomy, cavo-pulmonary anastomosis, dextrocardia, severe scoliosis, mechanical circulatory support (VAD due to failing systemic right ventricle in cc-TGA) and tricuspid valve dysplasia (Ebstein's anomaly); one patient suffered from Tetralogy of Fallot (TOF) with multiple previous surgery and another from juvenile HOCM. In 9 of 10 patients ICD was implanted due to secondary prophylaxis. Primary indication to opt for S-ICD as the first choice were: missing transvenous access (2), right-to-left shunt as contraindication for transvenous leads (4), avoidance of tricuspid valve passage (2) and young age without pacing indication (1). In one patient (with VAD) a pre-existing transvenous ICD had been removed due to chronic lead-associated infection and replaced by a right-sided S-ICD, combined with epicardial pacing. All patients were eligible by surface ECG template screening. Lead and device positioning was anatomically adapted and modified by pre-implant fluoroscopy to achieve an optimized intrathoracic electric field. Two systems were implanted in mirrored position in patients with dextrocardia, one lead was placed right parasternal and 9 of 10 devices implanted submuscular. Summary of results: After uneventful implantation successful DFT testing applying a 15 J safety margin confirmed correct function in all. Follow-up was performed up to 5 years. Cosmetic results were good with no pocket-related issues even in the smallest subjects. 3 patients – all with RBBB - suffered from inappropriate shocks due to altered T wave morphology under higher heart rate resulting in t-wave-oversensing (TWOS). This could be overcome by acquiring a new template under maximum exercise. The patient with TOF had multiple appropriate shocks from monomorphic VTs but also developed slow VTs below the shock zone (<170/min) and severe chronotropic incompetence. Therefore he was switched to a transvenous system with improved clinics due to the availability of pain free overdrive stimulation (ATP) and antibradycardiac pacing. The VAD patient died during follow-up of unknown reason. Conclusion: S-ICD therapy is feasible even in complex CHD patients, for whom conventional transvenous ICD concepts are not applicable. As this may avoid risks and burden associated with surgical lead placement, it represents an attractive new therapeutic modality. Due to the vast heterogeneity in size and anatomy, together with frequent alterations in excitation propagation and repolarization in this group, an advanced and thorough pre-implantation screening is mandatory. Modifications in lead and device arrangement supported by preoperative fluoroscopy are necessary, to ensure correct arrhythmia detection and therapy delivery even in distorted anatomy. The presumably higher incidence of TWOS has to be considered, although modified programming may resolve the issue. With submuscular placement, cosmetic and functional results are excellent; nevertheless the bulky size of the device currently precludes its use below a weight of approx. 30 kg. Despite successful application with combined (epicardial) pacing, the lack of antibrady- and -tachycardiac pacing currently represents the major limitation towards widespread use in the field of CHD.