It is clear that patients with malignancy, particularly adenocarcinomas, have an increased propensity to thrombosis. It also appears that patients with malignancy and thrombosis are relatively refractory to warfarin therapy and some may not respond ideally to heparin preparations. Occult malignancy in patients with unexplained thrombosis is of concern; however, the incidence varies with the age of the patient approaching 10% in those over 50 years of age. The extent of the evaluation for an underlying occult malignancy should be dictated by clinical judgment. Recurrent unexplained DVT, resistance to warfarin, and thrombosis of unusual sites are the major clues to significantly enhance the suspicion of an occult malignancy. In general, patients with thrombosis and malignancy need not be evaluated for hereditary or acquired hemostasis defects; finding one of these defects is both unlikely and will probably not alter antithrombotic therapy. Hemorrhage in cancer patients is usually due to thrombocytopenia related to chemotherapy (particularly solid tumors) or bone marrow failure (usually leukemias), or disseminated intravascular coagulation (DIC). DIC is usually seen in M-3 and M-4 leukemia or in septic patients with solid tumors. Finally, catheter thrombosis is a common problem in patients with cancer and can be significantly decreased with the routine use of low-dose warfarin therapy.