The incidence of tuberous sclerosis complex in Olmsted County, Minnesota, was 0.28 per 100,000 person-years from 1950 through 1989, the point prevalence on December 31, 1989, was 6.9 per 100,000 persons, and the incidence at birth was 6.0 per 100,000 live births. The incidence was 0.13 per 100,000 person-years from 1950 through 1974 and 0.46 per 100,000 person-years from 1975 through 1989. The higher rate of diagnosis during the later period is believed to be due to the use of computed tomography. Of the 12 patients considered in this study, one patient presented with seizures and severe intellectual disability, six patients presented with seizures, three patients presented with multiple facial angiofibroma, and two patients were asymptomatic.