Elderly patients require special consideration when administered anticoagulants because of age-related alterations in renal function, protein binding, and increased bleeding risk. Unfractionated heparin can be used in most patients but difficulties with dosing and monitoring often lead to inadequate anticoagulation. Low-molecular-weight heparin has more predictable pharmacokinetics than conventional heparin, but requires dose adjustments in renal impairment and obesity. Fondaparinux is a synthetic pentasaccharide that is being used increasingly for both treatment and prophylaxis of venous thromboembolism. The immune-mediated form of heparin-induced thrombocytopenia is a syndrome with thrombocytopenia or thrombosis in the setting of heparin use. Heparin-induced thrombocytopenia must be identified early, and treated with argatroban or lepirudin to avoid life-threatening complications.