The epidemiology of myasthenia gravis was studied in a Danish countryside county with 230,760 inhabitants. The incidence rate was 10.4 per million per year and the prevalence rate, 125 per million. The female to male ratio was 1.4 to 1. The diagnoses were delayed from a few hours to 6 years, most frequently on behalf of ophthalmologic diagnoses. A high incidence rate and a considerable diagnostic delay indicate that a number of patients suffering from myasthenia gravis are misdiagnosed, leading to unfortunate psychologic events.