The administration of anticoagulant thromboprophylaxis for all patients with cancer who are hospitalized for acute medical illness is considered standard practice and strongly recommended in clinical guidelines. These recommendations are extrapolated from randomized controlled prophylaxis trials not specifically conducted in cancer cohorts. Because hospitalized patients with cancer constitute a unique population with increased risk of venous thromboembolic events and major hemorrhage, validation of the efficacy and safety of primary thromboprophylaxis in this population is critical. We sought to summarize the rates of venous thromboembolic events and major bleeding episodes among hospitalized patients with cancer who were receiving anticoagulant therapy compared with placebo.