The incidence of tuberous sclerosis in Rochester, MN, was 0.56 per 100,000 person-years in 1950 through 1982, and point prevalence on December 31, 1980, was 10.6 per 100,000 persons. The true incidence and prevalence may be even higher, because cases with hypomelanotic macules and no other clinical manifestations are often unrecognized. Pertinent clinical observations in the eight cases identified included familial occurrence in two; hypomelanotic macules in all eight; seizures with onset before age 2 in four, of whom two were mentally retarded; and no neurologic abnormalities in those free of seizures.