Background Tourniquets used during total knee arthroplasty may lead to many complications. The aim of this study was to determine perioperative blood loss and its clinical relevance in total knee replacement surgery after applying a tourniquet.Methods From June 2009 to October 2009, 60 consecutive patients who underwent routine total knee arthroplasty were randomly divided into two groups and were treated with or without a tourniquet (30 patients/group). There were no significant differences in patient baseline characteristics between the two groups. We compared the two groups of patients in terms of intra- and postoperative bleeding, invisible or visible bleeding, and total blood loss.Results None of the patients showed poor wound healing, lower extremity deep venous thrombosis or other complications. The amount of blood loss during surgery was lower in the tourniquet group than in the control group (P＜0.01). However, postoperative visible bleeding (P ＜0.05) and occult bleeding (P ＜0.05) were significantly greater in the toumiquet group than in the control group. There was no significant difference in the total amount of blood loss between the two groups (P ＞0.05).Conclusions Tourniquet can reduce bleeding during total knee replacement surgery, but is associated with greater visible and invisible blood loss.