The acquired hypercoagulable states are responsible for a broad range of thrombotic and thromboembolic disorders. Symptoms and signs of acute ischemia or organ dysfunction will lead many of these patients to seek care in EDs. Proper diagnosis and therapy must be based on an understanding of epidemiology and pathophysiology. Immediate anticoagulation with heparin may not always be the treatment of choice; careful analysis of clinical and laboratory parameters is necessary to arrive at the safest and most effective course of action. Newer anticoagulants, including low-molecular-weight heparins and nonheparin compounds, are changing the therapeutic approach to many of these disorders.