The effect of the pneumatic tourniquet on the incidence of postoperative deep venous thrombosis is uncertain. We carried out a controlled study comparing the incidence of deep venous thrombosis when a tourniquet was used with the incidence when a tourniquet was not used. Thrombosis was detected by radioisotope venography. The results of the study showed no difference in incidence and we concluded that the pneumatic tourniquet has no influence on the formation of a thrombus in a deep vein.