Most episodes of acute pulmonary embolism completely resolve, through thrombolytic mechanisms. When adequate thrombolysis fails, however, residual obstruction to pulmonary vascular flow by fibrotic remnants may result in pulmonary hypertension. The genesis of this pulmonary hypertension is complex. Apart from the simple mechanical obstruction to blood flow that may occur from occlusion of significant areas of the pulmonary vascular bed, secondary vascular changes eventually may result from increased flow and pressure in nonobstructed areas of the lung, or factors generated by localized hypoxia in occluded segments. Chronic pulmonary hypertension from thromboembolism, regardless of the mechanism, is much more prevalent than is generally appreciated. Patients develop increasing shortness of breath, and the diagnosis is often missed. Pulmonary endarterectomy offers a cure for the condition, and wider recognition of the efficacy of the operation and the entity are therefore important. Pulmonary endarterectomy is a technically demanding procedure, now performed with success at only a handful of centers. However, with proper patient selection, meticulous surgical technique, and careful postoperative management, excellent results can be obtained. A true endarterectomy (not an embolectomy) of all affected parts of the lung is performed, and cardiopulmonary bypass, systemic cooling, and circulatory arrest are essential for the visibility necessary to clear all affected areas of the pulmonary vasculature. Medical treatment is ineffective for this condition, and the alternative surgical treatment is lung transplantation. Pulmonary endarterectomy appears to be permanently curative, though an inferior vena caval filter should be placed in all patients to prevent recurrence, and the patients must have life-long anticoagulation.