This is a literature review of the frequency of venous thromboembolism in hospitalized patients with cancer and of the available evidence supporting the use of thromboprophylaxis. Patients with cancer are at particularly high risk of venous thromboembolism and account for almost 20% of patients in the population. Hospitalization is an important risk factor in patients with cancer, with rates reported between 0.6% and 7.8%. The incidence has been increasing over the past decade. Three randomized controlled trials and meta-analyses indicate that prophylaxis with low molecular weight heparin, heparin, or fondaparinux significantly reduces the rate of venous thromboembolism in hospitalized medical patients who are at high risk. Patients with cancer were included in these studies, but prospective trials specifically focused on patients with cancer are not available. Evidence indicates that appropriate thromboprophylaxis is provided to a minority of hospitalized patients with cancer and that targeted educational efforts and computerized prompt systems can increase appropriate use. Guidelines developed by both oncology and thrombosis organizations support the use of thromboprophylaxis in hospitalized patients with cancer. In conclusion, most patients hospitalized with cancer are at high risk of venous thromboembolism, and thromboprophylaxis should be provided in the absence of active bleeding or a high bleeding risk.