Our knowledge of postoperative thromboembolic complications has increased enormously over the past 2 decades, particularly where diag­ nosis and prophylaxis are concerned. The 125 I-fibrinogen method of diagnosing thrombosis has completely changed our concept of the frequency, occurrence, and natural course of thrombosis, and it has formed the basis of most thromboprophylactic studies. Concurrently with the development of this diagnostic method, two methods for the prophylaxis of thrombosis have come into vo­ gue, namely low-dose heparin and dextran. Both these methods were tested in very extensive studies during the seventies, and their value has been unequivocally proved, for reducing both the frequency of thrombosis with and without symptoms, and the frequency of fatal pulmonary embolism. Thromboprophylaxis is not particularly common in surgery; how­ ever, and its general use is far from uncontested. It has been argued that not only does it complicate surgical activities and make them mo­ re expensive, but it also involves an unacceptable number of other complications.