PURPOSE: We assessed the feasibility of a large randomized trial intended to determine whether low-dose heparin prophylaxis given throughout hospitalization reduces mortality and morbidity in general medical patients. SUBJECTS AND METHODS: Hospitalized general medical patients aged more than 60 years at 5 Department of Veterans Affairs (VA) medical centers were randomized to receive enoxaparin 40 mg or identical placebo, given daily by subcutaneous injection until hospital discharge. Outcomes included total mortality at 90 days (the primary outcome) and 1 year, and occurrence in the VA hospital within 90 days of symptomatic deep venous thrombosis, pulmonary embolism, and major bleeding. RESULTS: Only 7.6% of hospitalized patients aged more than 60 years were eligible for the study, although a chart review had predicted 25%. The principal exclusions were prior indication for anticoagulation, anticipated need for anticoagulation, contraindication to heparin, expected hospitalization less than 3 days, and "supportive/palliative care only" status. We randomized 140 patients into each group, 28% of target recruitment. The groups were well matched by age and comorbidities. Death occurred in 13 patients receiving enoxaparin and 14 patients receiving placebo at 90 days (relative risk 0.93, 95% confidence interval 0.26-1.59), and in 36 and 32 patients, respectively, at 1 year (relative risk 1.13, 95% confidence interval 0.66-1.60). Clinical thromboembolic events occurred in 5 patients receiving enoxaparin and 8 patients receiving placebo, and major bleeding occurred in 2 and 5 patients, respectively. CONCLUSIONS: The pilot study indicated that the full study was not feasible. The decision to use prophylaxis pertains to only a small proportion of general medical patients hospitalized at VA medical centers, and this proportion is overestimated by chart review. The effect of low-dose heparin prophylaxis on clinical outcomes in hospitalized general medical patients remains uncertain. © 2006 Elsevier Inc. All rights reserved.