The effects of malignant diseases on the hemostatic system are complex and can manifest as either a hypercoagulable state or an increased bleeding risk. While traditionally linked more to patients with solid tumors, thrombotic events are now also recognized as significant complications in hematological malignancies, with a thrombotic rate comparable to that seen in solid tumors at high risk of thrombosis. Hemorrhages and untreated disseminated intravascular coagulation further add to the spectrum of hemostatic problems in cancer and can be fatal, as observed in acute leukemia.