Venous thromboembolism, including deep vein thrombosis and pulmonary embolism, is a major cause of morbidity and mortality. In most cases, one or more risk factors for removable or persistent venous thromboembolism can be identified. Persistent risk factors include inherited or acquired abnormalities of the hemostatic system and cancer. As Armand Trousseau first suggested, venous thromboembolism may be the first clinical manifestation of an occult cancer. This relationship has recently been confirmed by methodologically well designed studies. Furthermore, venous thromboembolism is the second cause of death in patients with clinically overt cancer. This review summarizes the state of the art of this association. The clinical trials described focus on the need to perform screening for occult cancer in patients with idiopathic venous thromboembolism. How extensive this screening should be is still matter of debate. On the other hand, patients with clinically overt cancer should be considered at high risk for developing venous thromboembolism, and adequate prophylaxis should be used.