In 2000, a total of 26,585,955 Medicare enrollees met the study inclusion criteria; in 2006, the total was 28,382,683. The number of hospitalizations for TKR among Medicare enrollees in the study increased from 145,242 in 2000 to 248,267 in 2006, and the overall TKR rate increased 58% (from 5.5 to 8.7 per 1,000 population). Similar increases were observed by sex, age group, and black or white race. In both years, the total number of procedures performed was highest among those aged 65-74 years, but the TKR rate was highest among those aged 75-84 years. TKR rates increased in all states from 2000 to 2006, with the greatest increases in Arkansas (84%), Mississippi (84%), and Delaware (83%), and the lowest increases in Iowa (35%), New Mexico (35%), and Idaho (38%). In 2006, TKR rates ranged from 13.9 in Utah to 4.5 in Hawaii.