Venous thromboembolic disease (VTED) occurs commonly in geriatric medical patients, causing significant morbidity and mortality. Although VTED is preventable, prophylactic anticoagulation is underused. Awareness of the clinical risk factors that contribute to VTED in the elderly is essential for identifying candidates for prophylaxis. Iatrogenic risk factors include venous catheterization, transvenous pacemaker placement, hormone replacement therapy, and immobilization or prolonged bed rest. Medical conditions associated with increased risk include a previous episode of VTED, myocardial infarction, heart failure, severe lung disease, cancer, and neurological conditions associated with paresis. Obstacles to the widespread usage of VTED prophylaxis in geriatric medical patients include the clinically silent nature of VTED, underestimation of the risk and clinical effect of VTED in this population, and concerns about the cost and safety of anticoagulant therapy in this population. Clinical practice guidelines devised specifically for geriatric medical patients facilitate rational use of thromboprophylaxis in this population. The safety, efficacy, cost-effectiveness, and convenience of low-molecular-weight heparins for thromboprophylaxis are reflected in their increasing prominence in clinical practice guidelines and clinical use.