The number of patients with myasthenia gravis diagnosed and registered in Norway from 1912-1981 has been collected, representing essentially all diagnosed cases during these 70 years. Until 1948, Oslo University Hospital, the National Hospital, had the only neurological department. in Norway. Since then, neurological departments have been established throughout our country. All these departments and all practising neurologists in Norway responded to the appeal for the necessary information on their diagnosed patients up to the end of 1981. The majority of the results are based on the period 1951-1981. The National Bureau of Statistics has registered the deaths of myasthenia gravis cases since 1951, and since 1956 where it has constituted an underlying or contributory cause. The incidence rate by diagnosis per million population 1951-1981 is 2.6 for males, 5.3 for females and 4 for both sexes. The prevalence per million population is 52 for males, 127 for females and 90 for both sexes. The mortality in males is 144% and in females 155% of the mortality in the population. The excess mortality is much greater in patients below 60 years of age, especially in females where a value of 483% if found.