Commentary Providers of health care are facing increasing pressure to decrease costs while maintaining or improving the quality of care. This is especially true in regard to total joint arthroplasty. The concept of offering bundled payments for an entire episode of care is shifting financial responsibility to surgeons and their institutions. Unfortunately, many physicians and administrators may not yet have sufficient information on, or an understanding of how to determine, the costs of care so as to assume this responsibility effectively1. The goal of the study by Palsis and colleagues was to increase our knowledge of how to determine the costs of total hip and total knee arthroplasty through an evaluation and comparison of 2 accounting methods: traditional cost calculation and time-driven activity-based costing (TDABC)2. The former method allocates total hospital costs, both direct and indirect, associated with the procedure. This represented a simpler and more practical approach. The latter method is based on only the direct costs of the resources utilized by an individual patient and was more complicated and time-consuming. It represents the theoretical ideal and did allow more accurate examination of the specific costs involved3. These 2 approaches generated major differences in cost estimates, with total costs for both total hip and total knee arthroplasty being considerably higher using the traditional method compared with TDABC. Cost estimates made using traditional accounting were roughly equal to the average Medicare reimbursement for hip replacement and greater than the Medicare reimbursement for knee replacement, whereas cost estimates made using TDABC were lower than the average Medicare reimbursement for both hip and knee replacement. The authors acknowledged that it was not possible to determine the “true costs” of total hip and knee arthroplasty, which they noted were likely to be between the estimates derived from the 2 methods, because of the many variables involved and the need to make certain assumptions, such as how to quantify indirect costs, for which there is no accepted standard. The data generated were based retrospectively on the work of 4 surgeons at 1 institution and were not intended to represent total joint arthroplasty in general. Using both methods, the high costs paid for consumable supplies and implants were accepted, without attempting to determine the possible savings that might result from selecting different components or negotiating lower prices. This is an interesting study that is both novel and timely and that provides certain information not previously available. It represents the expenditure of considerable time and effort by the authors. It does not attempt to provide definitive answers to specific questions but does help us understand the many factors to consider in the complicated process of determining the costs of total hip and knee arthroplasty. The study perhaps leaves us with more questions than answers but certainly does stimulate the reader to think about a clinically important issue. It should help health-care providers to function more effectively in addressing how to lower costs while maintaining or improving the quality of care4 and how to negotiate reimbursements from third-party payers more equitably. Additional studies along these lines are needed.