There has been a substantial change in the population demographics of patients who potentially will require total joint replacements. We studied data regarding temporal trends in physical condition, life expectancy, education, and other population demographics of individuals most likely to receive total joint replacements. Changes in this population during the last several decades correlate with temporal changes in the prevalence of joint disease and the incidence of total hip and knee replacements. Compared with several decades ago, patients currently receiving total joint replacements are almost 20% heavier, more physically active, three times more likely to have a high school or college education, and live more than 25% longer. Patients needing total joint replacements are more likely to be female, and twice as likely to receive a total knee replacement than a total hip replacement. Treatment choices and outcome expectations are best determined with accurate knowledge of current surgical science and current patient demographics. Therefore, it is important to realize that today's population most likely to receive total joint replacements is demographically different than in the past.