New joint replacement prostheses are being continually introduced into the market. The underlying purpose of the introduction of new devices is to improve patient outcomes. This study was undertaken to determine how many new prostheses were associated with improved patient outcomes. Data were obtained from a comprehensive national database. Outcome analysis was performed on all new hip and knee prostheses introduced into the market between January 1, 2003, and December 31, 2007, and used on at least 100 occasions. The findings were compared with the combined results of the three best performing established hip and knee prostheses with a minimum duration of follow-up of five years. The principal outcome measures were the rate of revision per observed component years and the time to first revision, with use of Kaplan-Meier estimates of implant survivorship. Most prostheses introduced into the market during the study period were used on fewer than 100 occasions. Analysis of those that had been used in a sufficient number of procedures showed that 27% (nine of thirty-three) of the hip replacements and 29% (eight of twenty-eight) of the knee replacements had a significantly higher rate of revision than the established prostheses. None of the newer prostheses had a lower rate of revision than the established prostheses. This study indicates that there was no benefit to the introduction of new prostheses into this national market during the five-year study period. Importantly, 30% of the new prostheses were associated with a significantly worse outcome compared with the prostheses with a minimal duration of follow-up of five years.