Background: Antibodies directed against acetylcholine receptor (AChR) are absent in approximately 15% of patients with gMG. Approved treatment options represent an unmet need in the AChR-antibody (Ab)- gMG population. Efgartigimod is an immunoglobulin G1 (IgG1) antibody Fc fragment that selectively reduces IgG levels by blocking neonatal Fc receptor (FcRn)-mediated IgG recycling. Here, we describe efgartigimod efficacy in AChR-Ab- participants with gMG receiving either efgartigimod IV or subcutaneous (SC) efgartigimod PH20 (coformulated with recombinant human hyaluronidase PH20) across clinical studies. Methods: Post hoc analyses were conducted to examine efficacy and safety of efgartigimod IV and/or efgartigimod PH20 SC in AChR-Ab- participants in ADAPT/ADAPT+ and ADAPT-SC/ADAPT-SC+ trials. Results: Among pooled AChR-Ab- participants (n=56), mean (SE) MG-ADL total score improvement from baseline to Week 3 was -3.7 (Cycle 1: 0.44 [n=55]). Consistent MG-ADL improvements occurred with repeated cycles. Clinically meaningful improvements (CMI; ≥2-point MG-ADL decrease) occurred in 76.4% (n=42/55) of participants (Cycle 1, Week 3). In Cycle 1, 23.2% (n=13/56) of participants achieved minimal symptom expression (MG-ADL 0-1). Similar efficacy results occurred across all cycles. Overall safety profile was similar between AChR-Ab+ and AChR-Ab- participants. Conclusions: Both efgartigimod IV and efgartigimod PH20 SC were well tolerated and led to CMI in participants with AChR-Ab- gMG.