We determined the incidence of status epilepticus (SE) by ascertaining all first episodes of SE in Rochester, Minnesota through the Rochester Epidemiology Project's records-linkage system between January 1, 1965 and December 31, 1984. Information was collected on age, gender, duration, seizure type, and etiology. The age-adjusted incidence of SE was 18.3 per 100,000 population. SE incidence was U-shaped, peaking under 1 year and over 60 years of age. The incidence of SE was greater for males than for females, for acute symptomatic etiology than any other etiology, and for partial SE that did not generalize than any other seizure type. Status of long duration(at least 2 hours) occurred more frequently among infants and the elderly than among persons aged 1 to 65 years. Cumulative incidence was 4 per 1,000 to age 75 and showed the greatest increase after age 60. Given the aging of the population, SE will become an increasingly important public health problem.