Acquired thrombotic risk factors include a variety of noninherited clinical conditions that can predispose an individual to an increased risk for venous thromboembolism. For patients in a critical care setting, certain acquired risk factors represent chronic conditions that the patients may have had before the current acute illness (e.g., malignancy, various cardiovascular risk factors, certain medications), whereas others may be directly related to the reason the patient is in an intensive care unit or the patient's management there (e.g., postoperative state, trauma, indwelling vascular access, certain medications). Optimal thromboprophylactic strategies depend on individual patient risk profiles including an assessment of the specific clinical setting. Treatment for patients with acquired thrombotic risk factors includes anticoagulant therapy and, if possible, resolution of the acquired risk factor(s). Heparin-induced thrombocytopenia represents a unique clinical situation in which all sources of heparin must be discontinued and the patient started on an alternative anticoagulant (e.g., a direct thrombin inhibitor) in the acute setting. The duration of anticoagulant therapy would vary depending on the specific clinical setting.