Abstract The manifestations of thromboembolism are highly variable and frequently obscure. Clinical diagnosis of these entities is difficult, and the majority of cases will not be diagnosed by the means presently available to us. Nevertheless, a heightened awareness of the vagaries of this disease can result in considerable improvement in diagnostic accuracy. Prompt diagnosis on the basis of the slightest clinical suspicion, followed by immediate and adequate anticoagulant therapy, should result in a measureable decrease in thromboembolic complications. However, if one hopes to achieve a profound reduction in incidence of thromboembolism, the only approach presently available is prophylactic rather than therapeutic. The use of measures to increase venous return in patients who are immobilized in bed, plus the institution of prophylactic anticoagulant therapy in a selected group of patients with a high predisposition to the development of thromboembolic diseases, should result in a significant reduction in disability and mortality from this theoretically preventable disease.