Background. Many patients in Ontario, despite being appropriate candidates for total joint arthroplasty (TJA), are not offered surgery. To understand this discrepancy, the authors sought to explore the process by which physicians determine patient candidacy for TJA. Methods. Six focus groups (2 each of orthopedic surgeons, of rheumatologists, and of family physicians) and subsequent in-depth interviews were conducted with 50 practicing clinicians in Ontario. Results. Health care system constraints, including extensive waiting lists, lack of homecare and postoperative support, and, for surgeons, access to operating rooms and resources, are perceived by physicians to routinely influence the ultimate choice of candidates for TJA. Medical brokering, defined as strategies used by physicians in a constrained health system to prioritize patients and to negotiate relationships with other physicians, was an important factor in determining candidacy for TJA. Because individual physicians and surgeons appear to use their own criteria for making these decisions, and because these criteria are modified from time to time in response to specific institutional and system conditions, brokering results in varied decisions about candidacy regardless of patient suitability. Conclusions. Lack of consensus on the necessary patient characteristics for TJA candidacy does not in and of itself account for the discrepancy between the number of patients who are suitable candidates for TJA and those who receive the procedure. Until the process by which health care system constraints affect and complicate the decision-making process around TJA candidacy is more fully explored, patients may not receive appropriate and timely access to this procedure.