Pulmonary embolism is the occlusion of pulmonary arteries by thrombi that originate elsewhere, typically in the large veins of the legs or pelvis. Risk factors for pulmonary embolism are conditions that impair venous return, conditions that cause endothelial injury or dysfunction, and underlying hypercoagulable states. Symptoms of pulmonary embolism are nonspecific and include dyspnea, pleuritic chest pain, and, in more severe cases, light-headedness, presyncope, syncope, or cardiorespiratory arrest. Signs are also nonspecific and may include tachypnea, tachycardia, and in more severe cases, hypotension. Diagnosis of pulmonary embolism is most commonly accomplished with CT angiography, although ventilation/perfusion scanning is sometimes required. Pulmonary embolism treatment is with anticoagulants and, sometimes, clot dissolution with systemic or catheter-directed thrombolysis or catheter or surgical removal. When anticoagulation is contraindicated, an inferior vena caval filter should be placed. Preventive measures include anticoagulants and/or mechanical compression devices that are applied to the legs in hospitalized patients.