We used Medicare administrative data to examine trends in primary and revision total hip arthroplasty (THA) use and hospital volume. Between 1991 and 2005, primary and revision THA use increased by 40.9% and 16.8%, respectively. The percentage of primary THA procedures performed in high-volume hospitals (those in the highest quintile of volume) increased slightly from 58.0% of all procedures in 1991 to 58.7% in 2005 (P < .01). The percentage of revisions performed in high-volume hospitals increased from 60.9% to 62.4% (P < .01). The percentage of primary THA procedures performed by low-volume hospitals remained relatively stable (P = .36), whereas the percentage of revision THA performed by low-volume hospitals declined (P < .001). In aggregate, these results suggest minimal evidence that regionalization of THA is occurring.