Over a period of four years, 23 patients had the diagnosis of chronic pulmonary hypertension made on the basis of elevated resting pulmonary arterial pressures above 30 mmHg mean. Clinical features included dyspnea (100%), previous thromboembolism (43%), congestive failure (39%), venous thrombosis (35%), syncope (30%), lung disease (22%), recent trauma (22%), hemoptysis (17%) and precordial pain (17%). Pulmonary angiograms showed embolic occlusion in all hut four patients, who were considered to have primary pulmonary hypertension. KimRay-Greenfield® vena caval filters were inserted in 18 patients. Three of them were in refractory shock at the time, and only the one who had successful intraluminal catheter embolectomy survived. These patients have been followed an average of 23 months with two embolic deaths, one from the right atrium and one bypassing a filter misplaced in the right iliac vein (overall mortality 22%). There has been no other known recurrent embolism, but one patient developed hematuria from the filter. The five patients who did not receive a filter have all died after intervals up to 18 months. Recurrent thromboembolism was documented in three and suspected in one patient with known embolic disease who died suddenly. Regardless of etiologic factors, pulmonary hypertension with cor pulmonale is associated with a high incidence of fatal thromboembolism. In our experience, maximal protection is afforded by long-term anticoagulation therapy and the placement of a venacaval filter.