Incidence of Crohn's disease in Olmsted County, Minnesota, 1935-1975.

The incidence, trend over a 41-year period, prevalence, familial aggregation, and survivorship of Crohn's disease in the population of Olmsted County, Minnesota, are described. During the period 1935-1975, there were 103 incidence cases; the age-adjusted incidence rate per 100,000 rose from 1.9 (1935-1954) to 4.0 (1955-1964) and to 6.6 in the most recent period (1965-1975). The increase of the rate over the last 11 years is due largely to the increase among persons 20 to 29 years old. No difference in the rates by sex was found. The urban rates were higher than the rural for both sexes and in each interval of the study. The prevalence of Crohn's disease among the residents of Olmsted County on Jan. 1, 1976, was found to be 105.7 per 100,000 population. The relatively high prevalence rate reflects the chronic nature of the disease, the recent increase of incidence, the completeness of case ascertainment, and the high survival rate among these patients.