Thrombosis and disseminated intravascular coagulation are common complications of cancer. Specific conditions associated with cancer such as stasis due to immobilization or blood flow obstruction, surgery, infections, endothelium damage due to chemotherapeutic agents and abnormalities of blood coagulation contribute to the hypercoagulable and thrombophilic state of cancer patients. This procoagulant state in cancer arises mostly from the capacity of tumor cells to express and release procoagulant activities (cancer procoagulant and tissue factor). Decreased levels of inhibitors of coagulation, impaired fibrinolysis, the presence of antiphospholipid antibodies and an acquired activated protein C resistance contribute to the hypercoagulable state. The activation of coagulation is also implicated in tumor proliferation through interactions of coagulation with inflammation and increased tissue factor pathway inhibitor. Laboratory diagnosis of the thrombophilic state include (1) elevation of clotting factors, fibrinogen/fibrin degradation products, hyperfibrinogenemia and thrombocytosis and (2) elevation of specific markers of activation of coagulation: fibrinopeptide A, fragment 1 + 2, thrombin-antithrombin complexes and D-dimers. However, none of the tests has any predictive value for the occurrence of thrombotic events in one individual patient. In patients with venous thromboembolism a noninvasive screening for occult cancer is able to detect a relatively high incidence of hidden cancer and the search for thrombophilia seems important in patients without known cancer.