Abstract The indications for unicompartmental arthroplasty are quite specific. Overall, there should be involvement of 1 tibiofemoral compartment, mild malalignment, and ligamentous stability. In a review of 250 osteoarthritic knees, these pathologic findings were present in 19 patients (8%). Technique, despite improvement in instrumentation, still is more demanding than tricompartmental knee arthroplasty, and failure to achieve an optimal arthroplasty occurs more frequently. In the literature, long-term results with unicompartmental arthroplasty have been inferior to tricompartmental arthroplasty. The concept that unicompartmental arthroplasty is a temporizing procedure is not a valid one in that the patient has to undergo another arthroplasty with all the risks of revision arthroplasty surgery. Many of these revision procedures require bone grafting or component augmentation. Tibial osteotomy remains the procedure of choice in younger, active patients with unicompartmental arthritis (in highly selected patients), and tricompartmental arthroplasty is preferred in older, lower demand patients. Copyright 2002, Elsevier Science (USA). All rights reserved.