Incidence of amyotrophic lateral sclerosis in three counties in western Washington state.

We conducted a population-based study of amyotrophic lateral sclerosis (ALS) in King, Pierce, and Snohomish counties in western Washington state. Between April 1, 1990 and March 31, 1995, neurologists diagnosed 235 patients with ALS, including 127 men (54%) and 108 women (46%). The incidence rate, age-adjusted to the 1990 total U.S. population, was higher for men at 2.1 per 100,000 per year (95% CI, 1.3 to 2.9) than for women at 1.9 (95% CI, 1.1, 2.7) and increased with age for both men and women. These incidence rates are consistent with other studies from northern latitudes.