There is an increased risk not only of bleeding but also of thrombosis in the cancer patient. The double jeopardy creates an additional problem in their management and requires special attention. This review provides information on pathophysiology in the regulation of hemostasis, leading to bleeding and thrombotic complications. The process is complex with multiple factors being involved. In addition to the pathogenesis, a number of clinical syndromes, diagnostic methods and the management of hemostatic abnormalities in the cancer patient are presented. Potential effects of cancer treatment on these risks magnify the hazards encountered by the managing team. Wherever management is discussed, emphasis is placed on the scientific basis for the rationale of the therapeutic approach.