Background: As an elective procedure, total knee arthroplasty is under scrutiny to evaluate its cost-effectiveness. In this review, we examined the available literature on total knee arthroplasty to assess the evidence regarding factors associated with better functional outcomes. Methods: A structured literature search of English-language databases was performed to identify studies of the functional outcomes of total knee arthroplasty that had been published between 1995 and April 2003. Inclusion criteria were a study of primary total knee arthroplasty, more than 100 knees in the study, provision of baseline data and rating of postoperative outcomes with a standardized symptom scale, and an experimental or quasi-experimental study design. The abstracting form included a list of potential prognostic factors, including comorbidities, radiographic evidence of joint destruction, bone loss, integrity of the extensor mechanism, range of motion, alignment, tibiofemoral angle, and ligament integrity, as well as the characteristics of the operating surgeon, such as procedure volume and experience. Results: Sixty-two studies met the criteria and were reviewed. Total knee arthroplasty was found to be associated with substantial functional improvement, with the effect sizes varying with the measure that was used. Physician-derived measures showed effect sizes of 2.35 and 3.91, whereas patient-derived measures showed smaller effect sizes (1.27 and 1.62). Few investigators used multivariate models to identify associations between outcomes and patient characteristics. Conclusions: Total knee arthroplasty is a generally effective procedure, but the current English-language literature does not support specific recommendations about which patients are most likely to benefit from it. Level of Evidence: Prognostic Level II.