The benefits of low-molecular-weight heparins (LMWHs) over heparin and warfarin in treating and preventing thromboembolic disorders are discussed. Numerous advantages are associated with using heparin for treating and preventing thromboembolic disorders. Heparin's short half-life allows for relatively easy and frequent adjustments of therapy. Warfarin has a long half-life and high bioavailability that allow for once-daily administration and a prolonged pharmacodynamic effect. However, approximately 3-5% of patients develop heparin-induced thrombocytopenia with potentially catastrophic complications. Warfarin also has numerous limitations, including frequent and specialized monitoring, an inherent variability in response over time, a propensity for altering the international normalized ratio, and the potential for causing errors in laboratory test values. LMWHs eliminate or reduce the major disadvantages of anticoagulant therapy with heparin and warfarin. The advantages of LMWHs over unfractionated heparins include an improved pharmacokinetic profile. LMWHs are recommended for treating deep vein thrombosis (DVT). They offer convenient administration and the potential for outpatient treatment. They may also result in a slightly lower rate of thromboembolism recurrence and extend the life of cancer patients. For DVT prophylaxis, LMWHs have demonstrated efficacy with 45-70% relative-risk reduction in patients undergoing total hip or total knee replacement and in patients with hip fracture. However, more data are needed for administration to special patient populations, such as the obese and those in renal failure. LMWHs eliminate or reduce the major disadvantages of anticoagulant therapy with heparin and warfarin for treating and preventing thromboembolic disorders. Further study is needed regarding their administration in special populations.