The prevention of venous thromboembolism (VTE) in patients recovering from major trauma, spinal cord injury (SCI), or other critical illness is often challenging. These patient groups share a high risk for VTE, they often have at least a temporary high bleeding risk, and there are relatively few thromboprophylaxis trials specific to these populations. A systematic literature review has been conducted to summarize the risks and prevention of VTE in these three groups. It is concluded that routine thromboprophylaxis should be provided to major trauma, SCI and critical care patients based on an individual assessment of their thrombosis and bleeding risks. For patients at high risk for VTE, including those recovering from major trauma and SCI, prophylaxis with a low molecular weight heparin (LMWH) should commence as soon as hemostasis has been demonstrated. For critical care patients at lower thrombosis risk, either LMWH or lowdose heparin is recommended. For those with a very high risk of bleeding, mechanical prophylaxis should be instituted as early as possible and continued until pharmacologic prophylaxis can be initiated. The use of prophylactic inferior vena caval filters is strongly discouraged because their potential benefit has not been shown to outweigh the risks or substantial costs. Implementation of thromboprophylaxis in these patients requires a local commitment to this important patient safety priority as well as a highly functional delivery system, based on the use of pre-printed orders, computer prompts, regular audit and feedback, and ongoing quality improvement efforts.Across the spectrum of hospitalized patients, the rates of venous thromboembolism (VTE) vary substantially.1 Although a large number of patient-specific thrombosis risk factors have been shown to contribute to this variability, the principal factor that determines VTE risk is the patient's primary reason for hospitalization, whether this is a surgical procedure or an acute medical illness. This paper will discuss the risks of VTE in three populations: major trauma, spinal cord injury (SCI) and critical care patients. The reasons for selecting these patient groups are as follows: each is associated with a high risk of VTE; there is often also a temporary high risk of bleeding; and there have been relatively few studies of prophylaxis in each of these groups. Despite the challenges involved in preventing VTE in these patients, recent evidence allows clinicians to provide effective and safe prophylaxis (see Figure 1).