OBJECTIVE: To study the rates of use of total hip arthroplasty (THA) and total knee arthroplasty (TKA) during the past 4 decades. METHODS: The Rochester Epidemiology Project was used to identify all Olmsted County, Minnesota, residents who underwent THA or TKA from January 1, 1969, through December 31, 2008. We used a population-based approach because few data are available on long-term trends in the use of THA and TKA in the United States. Rates of use were determined by age- and sex-specific person-years at risk. Poisson regression was used to assess temporal trends by sex and age group. RESULTS: The age- and sex-adjusted use of THA increased from 50.2 (95% confidence interval [CI], 40.5-59.8) per 100,000 person-years in 1969-1972 to 145.5 (95% CI, 134.2-156.9) in 2005-2008, whereas TKA increased markedly from 31.2 (95% CI, 25.3-37.1) per 100,000 person-years in 1971-1976 to 220.9 (95% CI, 206.7-235.0) in 2005-2008. For both procedures, use was greater among females, and the rate generally increased with age. CONCLUSION: In this community, TKA and THA use rates have increased steadily since the introduction of the procedures and continue to increase for all age groups. On the basis of these population-based data, the probable need for TKA and THA exceeds current federal agency projections. © 2010 Mayo Foundation for Medical Education and Research.