In a population of 100,000, between 3 and 8 people have ALS (prevalence). Two new cases of the disease occur annually, again with reference to a population of 100,000 (incidence). The frequency of ALS is similar worldwide. A much higher but now falling incidence has been found only in a few regions of the western Pacific.

The main age of disease onset is between 50 and 70 years. The youngest patients get the disease at the age of 20 to 30 years. The average age at onset is 56 to 58 years. Fewer than 10% of ALS patients develop the disease below the age of 40. Men are affected somewhat more often than women (about 1.5:1).