The incidence, trend, and survivorship of ALS in the population of Rochester, Minnesota, was determined for the years 1925 through 1977. The average annual incidence was 1.76 per 100,000 population. There was a small but nonsignificant increase in the rate during the 53-year period. The male:female ratio was 1.1, and the male:female ratio of incidence rates was 1.6. The median age at onset was 66 years; the incidence rates increased with increasing age. Median survivorship was 22.5 months, and was longer for younger patients than for patients with an advanced age at onset. The demographic characteristics in this total community experience are believed to reflect the pattern of ALS more accurately than previously reported clinical series.