The risk of venous thromboembolism (VTE) in medical patients is generally underestimated. However, recent studies including two large double-blind placebo-controlled trials, the Prospective Evaluation of Dalteparin Efficacy for Prevention of VTE in Immobilised Patients trial (PREVENT) and prophylaxis in MEDical patients with ENOXaparin, study show that low-molecular-weight heparins (LMWHs) provide effective thromboprophylaxis for medical patients at risk from VTE without increasing the risk of bleeding. In PREVENT the significant 45%, reduction in VTE among patients receiving dalteparin 5000 IU once daily for 14 days was attributed entirely to a reduction in clinically relevant VTE. The recently published guidelines for the prevention and treatment of VTE, issued by the American College of Chest Physicians, recommend prophylaxis with LMWHs (or low-dose unfractionated heparin) in acutely ill medical patients with risk factors for VTE (grade 1A). Current evidence should encourage the more widespread adoption of thromboprophylaxis in at-risk medical patients, and thus reduce the number of preventable deaths and complications due to VTE.