BACKGROUND: Hospitals in which a high volume of arthroplasty procedures are performed have been observed to have better outcomes. As the number of arthroplasties has increased, it is not known whether surgical cases have shifted to high-volume hospitals. In this study, we examined the change in the volume of arthroplasties to provide a contemporary definition of "high-volume" centers, quantified surgical volume that shifted to high-volume centers, and investigated the resulting effect on complications. METHODS: Data from the National (Nationwide) Inpatient Sample (2000 to 2012) were used to quantify trends in total hip arthroplasty (THA) and total knee arthroplasty (TKA) volume. Elective primary THAs and TKAs were identified and grouped by hospital by utilizing the hospital identifier, which indicates the geographic location of the hospital. County geographic and population data were obtained from the U.S. Census, and the distances between hospitals and the centroids of counties were calculated. Risk-standardized surgical complication rates for hospitals (2009 to 2012) were obtained from Medicare Hospital Compare and grouped by hospital volume. RESULTS: From 2000 to 2012, there was a marked increase in the number of hospitals that performed a combined volume of ≥400 elective primary THAs and TKAs. The number of elective primary TKAs and THAs performed annually increased from 343,000 to 851,000. In 2012, 65.5% of the arthroplasties were performed in high-volume hospitals (≥400 arthroplasties annually), and 26.6% of the arthroplasties were performed in very high-volume hospitals (≥1,000 procedures annually). The proportion of arthroplasties performed in low-volume hospitals (<100 arthroplasties annually) shrank from 17.9% to 5.4%. Very high-volume hospitals had the lowest complication rates (2.745 per 100; 95% confidence interval [CI], 2.56 to 2.93), and low-volume hospitals had the highest complication rates (3.610 per 100; 95% CI, 3.58 to 3.64; p < 0.0001) (odds ratio, 1.327; 95% CI, 1.26 to 1.40). Our analysis showed that 81.9% of the U.S. population lived within 50 miles of a high-volume hospital. CONCLUSIONS: Arthroplasty patients are electing to have their procedures at higher-volume hospitals in the United States. Each successively higher hospital volume category manifested a lower complication rate.