The association between thrombosis, bleeding and neoplastic disease is well recognized. There are distinctive features of the thrombotic and bleeding complications associated with specific hematologic malignancies. A number of procoagulants can initiate intravascular clotting including tissue factor, cancer procoagulant and interleukin-1. The hematologic malignancy most often associated with intravascular clotting and bleeding is acute promyelocytic leukemia. The pathogenesis of the life-threatening bleeding disorder associated with this uncommon subtype of acute myeloid leukemia (AML) is complex and involves disseminated intravascular coagulation, fibrinolysis and proteolysis. Both all-trans retinoic acid and arsenic trioxide result in relatively rapid resolution of the coagulopathy. Intravascular clotting may also be induced by hyperleukocytosis in AML and by the hyperviscosity syndrome observed in multiple myeloma and Waldenström's macroglobulinemia. In the setting of hematologic malignancies, when thromboembolic complications occur, the presence of comorbid thrombophilic conditions should be excluded. Abnormal platelet production and function contribute to the development of thrombosis in patients with myeloproliferative disorders. The Budd-Chiari syndrome may be observed in patients with myeloproliferative disorders. A number of medications have thrombogenic potential, including corticosteroids, thalidomide, L-asparaginase, all-trans retinoic acid and arsenic trioxide.