This population-based observational study examines the incidence, prevalence, and mortality rates of myasthenia gravis (MG) in Denmark, Finland, and Sweden from 2000 to 2020. The study uses nationwide health and administrative registries to identify patients with MG based on International Classification of Diseases codes. Key findings include: - **Incidence and Prevalence**: The overall incidence of MG was 1.34 per 100,000 in Denmark, 1.68 per 100,000 in Finland, and 1.62 per 100,000 in Sweden. The overall prevalence was 18.56 per 100,000 in Denmark, 20.89 per 100,000 in Finland, and 23.42 per 100,000 in Sweden. - **Mortality**: The standardized mortality ratio (SMR) for MG patients was 1.32 in Denmark, 1.23 in Finland, and 1.20 in Sweden. The SMR was higher in women than in men. - **Causes of Death**: The most common causes of death among MG patients were MG itself, chronic ischemic heart disease, and acute myocardial infarction. - **Factors Associated with Mortality**: The risk of death increased with age and duration of disease but decreased slightly over time. Patients with certain comorbidities, such as blood and blood-forming organ diseases, respiratory diseases, metabolic diseases, and thymoma, had an increased risk of death. The study highlights the need for improved care, particularly for young women with MG, to reduce morbidity and mortality.This population-based observational study examines the incidence, prevalence, and mortality rates of myasthenia gravis (MG) in Denmark, Finland, and Sweden from 2000 to 2020. The study uses nationwide health and administrative registries to identify patients with MG based on International Classification of Diseases codes. Key findings include: - **Incidence and Prevalence**: The overall incidence of MG was 1.34 per 100,000 in Denmark, 1.68 per 100,000 in Finland, and 1.62 per 100,000 in Sweden. The overall prevalence was 18.56 per 100,000 in Denmark, 20.89 per 100,000 in Finland, and 23.42 per 100,000 in Sweden. - **Mortality**: The standardized mortality ratio (SMR) for MG patients was 1.32 in Denmark, 1.23 in Finland, and 1.20 in Sweden. The SMR was higher in women than in men. - **Causes of Death**: The most common causes of death among MG patients were MG itself, chronic ischemic heart disease, and acute myocardial infarction. - **Factors Associated with Mortality**: The risk of death increased with age and duration of disease but decreased slightly over time. Patients with certain comorbidities, such as blood and blood-forming organ diseases, respiratory diseases, metabolic diseases, and thymoma, had an increased risk of death. The study highlights the need for improved care, particularly for young women with MG, to reduce morbidity and mortality.