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To estimate the minimal clinically important difference (MCID) for the MG-QOL15R. Data from two multi-country myasthenia gravis studies were used: the ADAPT RCT (n = 157) and the MyRealWorld-MG (MRW-MG) survey (n = 92). MCIDs were estimated using four anchor-based methods: change difference (CD), receiver operating characteristic (ROC) curve with Area Under the Curve (AUC), linear regression, and equipercentile linking. MG-Activities of Daily Living (MG-ADL) was the anchor. MCIDs were applied to the ADAPT RCT to assess the impact of different thresholds. Odds ratios (ORs) and 95% confidence intervals (CIs) were calculated to estimate the odds of achieving an MCID threshold at week 4 in the efgartigimod arm compared with placebo among patients positive for acetylcholine receptor antibodies. Baseline mean age was 46.7 years old in ADAPT and 49.8 years old in MRW-MG; women comprised 71.3% and 71.7%, respectively. ADAPT included only generalized MG, while MRW-MG included 12.0% ocular and 88.0% generalized MG. Average disease severity (MG-ADL 9.0 vs. 6.3) and HRQoL impairment (MG-QOL15R 16.3 vs. 12.0) were greater in ADAPT. MCID estimates were: CD (ADAPT 1.6; MRW-MG 2.8), ROC (both 2.5, AUCs 0.66; 0.71), linear regression (2.1; 1.6), and equipercentile linking (2.0; 3.0). Applying MCIDs of ≥ 2.0 and ≥ 3.0 resulted in ORs of 3.31 (95%CI 1.65–6.87) and 4.14 (95%CI 2.11–8.38). MCID estimates ranged between 1.6 and 3.0 across both studies. MCID thresholds of 2- and 3-points may indicate a minimal clinically meaningful change for monitoring progress and guiding treatment. Future research should use patient global impression of change anchors to improve interpretability and clinical relevance of MCID estimates. People with Myasthenia Gravis (MG), a rare disease that causes muscle weakness, often face problems that affect their daily lives and overall well-being. To better understand how MG impacts people and whether treatments are working, health professionals use a questionnaire called the MG-QOL15R. This tool captures key aspects of patients’ experiences with MG. However, it is unclear how much a person’s score needs to change for that change to be considered meaningful. This study looked at how much change in the MG-QOL15R score is needed to reflect a real difference in someone’s health. We used data from two international studies involving people living with MG and tested different ways to determine what amount of change matters to patients. We found that a change between 2 and 3 points on the MG-QOL15R is likely to be minimally meaningful. Smaller changes may reflect early improvement, while larger changes are more reliable for guiding treatment decisions. These findings can help doctors, researchers, and policymakers understand whether a treatment is truly helping people with MG feel better.