The effects of using a tourniquet during total knee arthroplasty were studied in 80 patients randomly allocated to two groups, either with or without a tourniquet. The groups were similar in mean age, gender, preoperative knee score and radiographic grading and the patients were all operated on by the same surgeon using one type of prosthesis. There was no significant difference between the two groups in operating time or total blood loss but postoperative pain was less in the patients in whom a tourniquet had not been used. They achieved straight-leg raising and knee flexion earlier and had fewer superficial wound infections and deep-vein thromboses. Total knee arthroplasty can be safely performed without the use of the tourniquet with the benefit that several adverse effects associated with its use can be avoided.