The overall incidence of postoperative DVT in patients with cancer is twice as high as in cancer-free patients. Immobilisation and chemotherapy increase the risk of thrombosis as does the insertion of central venous lines. Patients with cancer who have established thrombosis exhibit a remarkably high risk of recurrent thromboembolism, particularly in the first months after the interruption of anticoagulant treatment: the risk is double that of non-cancer patients. Even during anticoagulant treatment, the cumulative incidence of recurrent thromboembolism is 3.5 times higher in patients with malignancy than in cancer-free patients. Conversely, there is a high rate of cancer detection in patients with idiopathic VTE: the risk of concomitant cancer is approximately four times higher in these patients than in those with thrombosis triggered by known factors. Extensive screening for cancer in patients with idiopathic venous thrombosis allows early detection of malignancies and identification of malignancy at an early stage.