Total knee arthroplasty (TKA) is being used increasingly for the management of chronic arthritis of the knee. In this report, we review the frequency of application of TKA in the population of Olmsted County, Minnesota, from 1971 through 1986. The utilization rate of TKA increased from 20.5 per 100,000 person-years for 1971 through 1974 to 60.8 per 100,000 for 1983 through 1986. Although rates were higher in women, they increased with advancing age in both sexes. Rates between the urban and rural populations of Olmsted County did not differ. The two most common underlying diseases that necessitated TKA were osteoarthritis and rheumatoid arthritis; they were the cause of more than 90% of all operations. By extrapolating the rates of TKA in Olmsted County to the total 1986 US population, we estimate a need for at least 143,000 TKAs annually at a direct cost of more than $2.3 billion each year.