Assessment of risk for the development of venous thromboembolism (VTE), selection of VTE prophylaxis in medical patients, strategies for improving prescribing practices to prevent VTE, and the impact of pharmacist-managed anticoagulation services are described; case studies are used to illustrate each topic. Assessing risk for VTE is more complicated for acutely ill medical patients than for surgical patients. The risk of VTE in medical patients increases with the number of VTE risk factors the patient has. A number of regimens have demonstrated efficacy in reducing the rate of VTE in medically ill patients. Head-to-head studies suggest that enoxaparin 40 mg daily is at least as effective as unfractionated heparin (UFH) 5000 units three times daily for preventing VTE in acute medically ill patients. Because of greater efficacy, enoxaparin may be preferred over UFH in certain patient populations at particularly high risk for VTE. Although the efficacy of VTE prophylaxis is well documented, most patients at risk still do not receive this therapy. A combination of strategies is more effective than a single strategy for modifying prescribing practices to ensure that optimal VTE prophylaxis is provided when indicated. Pharmacist-managed anticoagulation services improve the appropriate use of anticoagulant agents, shorten hospital length of stay, and reduce mortality, drug-related complications, hospital readmissions for bleeding and thrombosis, and costs. Pharmacists can improve clinical and economic outcomes in acutely ill medical patients who are at risk for VTE through the use of various strategies, including anticoagulation management services.