The aim of this study was to identify the clinical factors associated with the need for peri-operative blood transfusion in non-anaemic patients undergoing hip or knee arthroplasty. We prospectively evaluated 162 consecutive patients who underwent total hip or knee arthroplasty. Analysis was performed to establish the relationship between all independent variables and the need for postoperative transfusion. Univariate analysis revealed a significant relationship between the need for postoperative blood transfusion and the pre-operative haemoglobin levels (P = 0·001), weight (P = 0·019) and age (P = 0·018). Multivariate analysis identified a significant relationship only between the need for transfusion and the pre-operative haemoglobin level (P = 0·0001). The pre-operative haemoglobin level of the patient was the only variable to independently predict the need for blood transfusion after primary hip or knee arthroplasty.