The MG-QOL15 is helpful in informing the clinician about the patient's perception of the extent of and dissatisfaction with myasthenia gravis (MG)-related dysfunction. The aims of this study were to determine the usefulness of the MG-QOL15 for following individuals with MG and to guide clinical researchers who plan to use the MG-QOL15. We assessed sensitivity and specificity for detecting clinical change and evaluated test-retest reliability. Sensitivities and specificities of various cut-points of change in scores are presented. Also presented are means and standard deviations of MG-QOL15 scores for all patients and for subgroups of patients. The test-retest reliability coefficient was 98.6%. The MG-QOL15 has an acceptable longitudinal construct validity. We consider this instrument to be most useful for informing the clinician about the patient's perception and tolerance of MG-related dysfunction. More objective measures, such as the MG Composite, should also be used to follow disease severity.