We report a case of a 70-year-old man with chronic thromboembolic pulmonary hypertension (CTEPH) in whom bronchial asthma had been clinically diagnosed and treated, and who showed remarkable improvement by pulmonary endarterectomy. He had dyspnea on exertion and had been clinically treated for bronchial asthma for 15 years. However, his symptoms did not improve after oral and inhaled corticosteroid therapy, and he had dyspnea at rest. CTEPH was suspected by echocardiography and computed tomography (CT) and he was admitted to our hospital. Perfusion scans showed multiple segmental perfusion defects with normal ventilation study, and contrast-enhanced CT showed intramural thrombi in both pulmonary arteries. Right cardiac catheterization revealed a mean pulmonary arterial pressure of 70 mm Hg and pulmonary vascular resistance of 1699 dyn.s.cm(-5) with chronic thromboembolic findings on pulmonary angiography. After surgery his pulmonary hemodynamics and symptoms significantly improved. CTEPH is rarely diagnosed at the initial visit because the only symptom is dyspnea on exertion, and it is often misdiagnosed as other respiratory diseases. But it is important to suspect and diagnose CTEPH in patients with unexplained dyspnea because this disease can be cured by surgery.