Patients undergoing total knee arthroplasty (TKA) are likely to receive a blood transfusion, which may increase the risk of complications and prolong hospital stay. Considerable variation exists in transfusion practice among orthopedic surgeons following elective TKA. Previous studies have investigated the relationship between preoperative risk factors and the requirement for blood transfusions in patients undergoing a total hip or knee arthroplasty, but few have focused on transfusion risk in those specifically undergoing TKA.The authors performed a retrospective review of a prospectively collected database of 2281 patients undergoing unilateral TKA in a district general hospital over a 10-year period. Multiple regression analysis models were used to identify risk factors associated with postoperative blood transfusion. A predictive model was created based on the regression coefficients and factor levels. The risk of transfusion was independently predicted by the patients' age at surgery (P<.001), preoperative hemoglobin (P<.001), weight (P=.009) and lateral retinacular release (P<.001). The preoperative variables of age, hemoglobin, and weight were incorporated into a model to provide an estimation of the transfusion risk. The area under the receiver operating characteristic curve was 74% (95% confidence interval, 70%-77.5%). This study identifies risk factors independently associated with the risk of requiring a blood transfusion following TKA. The predictive model stratifies the risk according to the individual patient in the preoperative setting, allowing preventative measures to take place preoperatively. It also helps in the counseling of patients at high risk of requiring a postoperative blood transfusion.