OBJECTIVE: A major component of the economic burden associated with the treatment of arthritis relates to surgical joint replacements of the hips/knees. The purpose of this study was to describe the recent trend of hip/knee replacements and the associated economic burden. METHODS: The Nationwide Inpatient Survey from 1997 to 2004 was analyzed. The International Classification of Diseases, Ninth Revision, Clinical Modification procedure coding was used to identify joint replacement cases. RESULTS: During 2004, approximately 225,900 (95% confidence interval [95% CI] 201,782-250,018) primary hip replacements and 431,485 (95% CI 397,454-465,516) primary knee replacements were performed. This was a 37% increase in primary hip replacements and a 53% increase in primary knee replacements compared with 2000. The number of primary replacement procedures increased equally for males and females; however, the number of procedures increased excessively among persons age 45-64 years. While Medicare remained the major source of payment (55.4% for primary hip replacements, 59.3% for primary knee replacements), private insurance payment experienced a steeper increase. In 2004, the national bill of hospital charges for hip/knee replacements was $26.0 billion, the hospital cost was $9.1 billion, and the amount of reimbursement was $7.2 billion (28% of hospital charges or 79% of hospital cost). Nearly 600,000 hip replacements and 1.4 million knee replacements will be performed in the year 2015. CONCLUSION: The number of joint replacement procedures performed is growing faster than ever. The health care community should consider and prepare for this upcoming demand of surgical loads and its associated economical burden.