Critically ill patients are at increased risk of developing venous thromboemboli (VTE). Risk factors that predispose them to acquiring VTE encompass factors that usually afflict the general medical population as well as factors attained in the intensive care unit (ICU) (e. g., sedation, mechanical ventilation). The poor cardiopulmonary reserve of this patient population is intolerant of even small pulmonary emboli (PE), which emphasizes the importance of preventing VTE from ever occurring. Indeed, the complications associated with hospital-acquired VTE increase morbidity, mortality, hospital length of stay, and costs. Without thromboprophylaxis, the incidence of VTE in the ICU ranges from 15 to 60%. Systematic implementation of VTE prophylaxis significantly reduces this rate and as a consequence, morbidity and mortality. In fact, prevention of VTE is so important that the American College of Chest Physicians (ACCP) developed guidelines on the use of routine VTE prophylaxis in critically ill patients. Therefore, upon admission, all ICU patients should be evaluated for and immediately prescribed the appropriate thromboprophylaxis therapy.