BACKGROUND: Chronic thromboembolic pulmonary hypertension most often results from obstruction of the pulmonary vascular bed by nonresolving thromboemboli. Misdiagnosis of the disease is common because patients often present with subtle or nonspecific symptoms. Furthermore, some features in chest imaging may mimic parenchymal lung disease. The most clinically important mimic in high-resolution chest tomography is air trapping, which can be seen in a variety of small airway diseases.CASE REPORT: We present the case of a 45-year-old woman with a long history of dyspnea and exercise intolerance, misdiagnosed with allergic alveolitis. The diagnosis of CTEPH was finally established with computed tomography (CT) angiography and hemodynamics.CONCLUSIONS: Chronic thromboembolism is under-diagnosed and also frequently misdiagnosed in clinical practice. The present report aims to increase the awareness of clinicians towards an accurate diagnosis of the disease, which is necessary for the early referral of CTEPH patients for operability.