From 1935 through 1982, keratoconus was newly diagnosed in a total of 64 residents (35 males and 29 females) of Olmsted County, Minnesota. There were no significant trends in incidence rates over time; the overall average annual rate was 2.0 per 100,000 population. The age-specific incidence rates were greatest in the younger groups. The incidence rates did not differ significantly by sex. On Dec. 31, 1982, the overall prevalence rate was 54.5 per 100,000 population. At the time of diagnosis, keratoconus was unilateral in 26 patients (41%) and bilateral in 38 patients (59%). Follow-up of the patients showed that survival did not differ significantly from that of the general population. The cumulative probability of survivorship without corneal transplantation for more than 20 years after diagnosis was greater than 80%.