The association between cancer and venous thromboembolism (VTE) is well established. Importantly, VTE is a significant cause of mortality in cancer patients. Although long-term warfarin (Coumadin(trade mark); Bristol-Myers Squibb; New York, NY) therapy is the mainstay of treatment for cancer patients with VTE, there are many practical problems with its use in this population. In particular, achieving therapeutic drug levels is difficult in cancer patients due to the increased risk of drug interactions, malnutrition, vomiting, and liver dysfunction in these patients. Moreover, cancer patients are at an increased risk of adverse effects of warfarin therapy. In contrast, low-molecular-weight heparins (LMWHs) are associated with a lower risk of adverse events compared with warfarin in patients with cancer. These agents also offer practical advantages compared with warfarin, including more predictable anticoagulant effects and ease of administration in addition to possible antineoplastic effects. Several LMWHs have demonstrated superior efficacy to warfarin in the secondary prevention of VTE. In particular, the LMWH, dalteparin (Fragmin; Pfizer; New York, NY), has recently been shown to have superior efficacy to warfarin in a large trial of patients with cancer and VTE without increasing the risk of bleeding. A randomized trial of dalteparin has also shown improved response rates and survival in patients with small cell lung cancer. In view of the availability of more effective and reliable alternatives to warfarin therapy in cancer patients, it is appropriate to reassess the role of warfarin therapy in patients with cancer and VTE. Further evaluation of the LMWHs for effects on cancer outcome is indicated.