Pulmonary thromboembolism is a widespread problem and is an important cause of death in patients with a variety of medical and surgical conditions. There have been few significant advances in the understanding of the aetiology beyond additional evidence confirming the importance of Virchow's triad. An impressive list of epidemiological associations has been compiled, however. Some knowledge of the natural progression of the disease is required as an aid in the understanding of the application of the therapeutic and prophylactic measures available in the management of pulmonary embolism. It would seem that at least two-thirds of pulmonary emboli are non-fatal, and in these cases the natural resolution, even of comparatively large embolic masses, is very efficient in patients without pre-existing cardiopulmonary disease. Diagnosis may prove difficult and most ancillary investigations are of questionable value. On the other hand, pulmonary radio-isotope scanning is far more specific and pulmonary angiography is a comparatively simple and complication-free diagnostic procedure. Prophylaxis is a real and practical aim, especially following surgery or myocardial infarction. In these groups widespread clinical trials of prophylactic measures have been made possible by the objective radio-iosotope screening techniques. Mechanical means of preventing venous stasis and anticoagulation appear effective. In addition, low-dose subcutaneous heparin seems to be as useful as heparin in conventional dosage. Apart from conventional supportive therapy, there are three major approaches to the treatment of pulmonary embolism. Heparin remains the mainstay, particularly in the less severe cases, hopefully preventing propogation of thrombosis and recurrence of embolism, thus allowing resolution to take place. Thrombolytic therapy with streptokinase or urokinase is capable of producing far more rapid dissolution of pulmonary emboli with consequent theoretical advantages over heparin. No reduction in mortality has been shown using thrombolytic therapy. Patients who fail to respond satisfactorily to acute resuscitative measures may require pulmonary embolectomy.