Medical patients represent the majority of hospitalized patients, and at least 75% of fatal pulmonary emboli occur in this group. Medical patients are at significant risk of thromboembolic disease, yet few are considered for thromboprophylaxis. Recent studies have identified the risk factor profiles in this group of patients, and a risk assessment model for medical patients has been developed. Risk stratification will help to ensure that patients receive appropriate thromboprophylaxis. It is clear that patients with severe chronic respiratory disease, congestive heart failure, and infectious disease are at high risk of symptomatic venous thromboembolism (VTE), particularly pulmonary embolism. Heparin-based prophylaxis significantly reduces the incidence of VTE. Low-molecular-weight heparin offers a safe and cost-effective alternative to unfractionated heparin in medical patients; to date, enoxaparin is the only low-molecular-weight heparin licensed for thromboprophylaxis in this indication.