Aim <p>This study evaluated the efficacy and safety of the subcutaneous implantable cardioverter defibrillator (S-ICD) in patients with obesity.</p> Methods <p>In this bicentric, retrospective study, S-ICD recipients were divided into two groups based on body mass index (BMI: &lt; 30&#xa0;kg/m² and ≥ 30&#xa0;kg/m²). Defibrillation testing (DFT) failure, shock impedance, rates of appropriate and inappropriate shock, long-term complications, survival, and device-related or cardiac rehospitalizations were compared.</p> Results <p>Of the 120 patients included, most baseline characteristics were similar between patients with (<i>n</i> = 30) and without obesity (<i>n</i> = 90), except for a higher prevalence of diabetes in the group with obesity. The first shock during DFT was similarly effective (99 vs. 100%), although, shock impedance was significantly higher in patients with obesity (59 vs. 74 Ω; <i>p</i> = 0.011). There was no difference between the groups regarding the incidence of appropriate (hazard ratio [HR] 0.70, 95% confidence interval [CI] 0.21–2.34, <i>p</i> = 0.584), and inappropriate shocks (HR 0.92, 95% CI 0.23–3.48, <i>p</i> = 0.902). Non-infectious complications occurred numerically more often in obese patients (16.7% vs. 4.9%, <i>p</i> = 0.058), while device-associated infections were more frequent among non-obese patients (7.4% vs. 0%, <i>p</i> = 0.188). The risk of all-cause mortality (HR 0.32; 95% CI 0.11–0.97; <i>p</i> = 0.141), device-related (HR 0.52; 95% CI 0.14–1.90; <i>p</i> = 0.395) or cardiac rehospitalization (HR 1.06; 95% CI 0.48–2.32; <i>p</i> = 0.890) were similar between the groups.</p> Conclusion <p>Despite higher shock impedance during DFT at S-ICD implantation, shock efficacy remained stable during implantation and follow-up in both groups. Fewer infectious but more system-specific complications may manifest in patients with obesity compared to non-obese patients.</p> Graphical Abstract <p></p>