BACKGROUND: The PRAETORIAN (Prospective Randomized Comparison of Subcutaneous and Transvenous Implantable Cardioverter Defibrillator Therapy) and ATLAS (Avoid Transvenous Leads in Appropriate Subjects) trials demonstrated a reduction in lead-related complications with subcutaneous compared with transvenous implantable cardioverter-defibrillators (ICDs) in patients with standard ICD indications. However, they were not individually powered to assess differences in inappropriate shock. OBJECTIVES: The aims of this study were to compare the rates of a first inappropriate shock between subcutaneous and transvenous ICDs and to explore the underlying causes. METHODS: An individual participant data meta-analysis of PRAETORIAN and ATLAS was performed, using Cox regression models stratified by trial. The primary endpoint was time to first inappropriate shock. RESULTS: The pooled modified intention-to-treat population included 1,342 patients (median age 58 years, 21.8% women, 77.7% with primary prevention indications) who had been randomized to subcutaneous or transvenous ICDs. A proprietary algorithm aimed at reducing inappropriate shock was activated at baseline or at some point during follow-up in 77.1% of patients with subcutaneous ICDs. During a median follow-up period of 3.5 years, a first inappropriate shock occurred more frequently in patients randomized to subcutaneous compared with transvenous ICDs (2.5 vs 1.5 per 100 patient-years; HR: 1.61; 95% CI: 1.06-2.45; P = 0.03). Patients with subcutaneous ICDs had a higher hazard of first inappropriate shock due to cardiac oversensing (HR: 15.07; 95% CI: 3.60-63.15; P < 0.001) and electromagnetic interference or myopotentials (HR: 8.19; 95% CI: 1.88-35.64; P = 0.005) but a lower hazard of first inappropriate shock due to atrial arrhythmia (HR: 0.37; 95% CI: 0.19-0.71; P = 0.003). CONCLUSIONS: Although first inappropriate shocks were infrequent overall, they were more common with subcutaneous ICDs. First inappropriate shocks due to cardiac oversensing and electromagnetic interference were more common with subcutaneous ICDs, while first shocks due to atrial arrhythmia were more common with transvenous ICDs.