Myasthenia gravis affects all races and can develop at any age from childhood to old age. Women are affected nearly three times more often than men during early adulthood (under 40 years of age). After 50 years of age, more men are affected than women. It is fairly unusual for children under the age of 15 to have myasthenia gravis, except in some Asian countries where up to half of people with myasthenia gravis have symptoms beginning in childhood.

A 2009 survey found that 2,574 people in Australia were currently being treated for myasthenia gravis. This equals approximately 1.2 out of every 10,000 people.

Of course this survey is now 11 years old and the increase in people with MG in Australia has increased. There are also those that have MG and have not been diagnosed or have incorrectly been diagnosed.