OBJECTIVES: Total joint replacements are important surgical interventions for treating severe arthritis of weight-bearing joints. The most common indication for total knee replacement (TKR) is osteoarthritis of the knee joint. The goals of this study were to assess the trend in rate of TKR in Wisconsin and to describe the economic impact of these surgical procedures on the health care system. METHOD: A population-based cross-sectional study of TKR surgeries was conducted among Wisconsin residents aged > or = 45 years. The Wisconsin inpatient hospital discharge data from 1990 through 2000 were used. Rates were age-adjusted to the 2000 U.S. population, and charges for TKR were adjusted for inflation. RESULTS: From 1990 through 2000, the age-adjusted rate for TKR increased by 81.5% (from 162 to 294 per 100,000; p<0.001). The rate increased the most among the youngest age group (45-49 years), rate ratio 5.1 for men, 4.2 for women. The total charges for TKR increased from 69.4 million dollars to 148 million dollars (109.2% inflation-adjusted increase). Medicare received the highest proportion of charges for TKR procedures, but throughout the study period, the proportion of charges covered by private insurance increased by 39%. CONCLUSIONS: The rate and costs of TKR procedures among Wisconsin residents increased substantially from 1990 through 2000, especially among younger age groups. Changes in medical practices probably accounted for some of this increase, but these trends also may reflect an increased prevalence of osteoarthritis, which in turn may be related to dramatic increases in the number of individuals who are overweight.