PURPOSE:To investigate the population-based prevalence of keratoconus in US individuals aged 65 years and older. DESIGN:Multiyear retrospective cross-sectional claims analysis. METHODS:Fee-for-service claims from a 5% national sample of Medicare beneficiaries aged 65 years and older were reviewed. Claims records were queried on an annual basis for the years 1999 through 2003 for ICD-9 codes specific to keratoconus. The number of beneficiaries with keratoconus-related claims was counted for each calendar year. RESULTS:The number of beneficiaries receiving care for keratoconus rose steadily from 15.7/100,000 beneficiaries in 1999 to 18.5/100,000 in 2003, averaging 17.5/100,000 across the 5 years of the study. Keratoconus rates declined with increasing age but did not differ by gender. Keratoconus care was more prevalent in whites than in other races. CONCLUSIONS:Keratoconus is an uncommon disease in the Medicare population. Longitudinal analysis of Medicare claims data may provide a useful tool for monitoring uncommon diseases, such as keratoconus, in the elderly.