Conclusion: Active cancer is often associated with hypercoagulable state, which pertubs the hemostatic balance between anticoagulant and procoagulant forces, creating a prothrombotic state. The interaction between tumor cells and host cells involves direct cell-cell interaction or indirect mechanism by cytokine release. Hypercoagulable state in patients with malignant disease may result in the occurence of various clinically identifiable hemostatic system disorders: the most frequent one is venous thromboembolism (so-called secondary thrombosis). In cases of idiopathic venous thromboembolism, it is recommended to carry out specific clinical check-up to prove or to preclude asymptomatic malignant diseases.