WOS: 000330470200013 PubMed: 23823265 Bronchogenic cysts (BCs) can be life threatening if they compress vital structures in infants and small children. In particular, subcarinal cysts can be life-threatening and compromise the airways. In infants, the initial presentation may be respiratory distress. We report a case of mediastinal cystic mass compressing the main left bronchus. The case was an 18-month-old boy who had been admitted with acute respiratory distress. Chest x-ray showed overdistension of the left lung and a mediastinal shift. Foreign body aspiration was diagnosed. Magnetic resonance imaging was performed, which has shown a mediastinal cystic mass; therefore, the patient underwent thoracotomy. Surgical intervention revealed a subcarinal extrapulmonary BC that compresses the left main bronchus. The diagnosis of BC was confirmed with pathological investigation. In this report, we present a case of BC with the emphasis on the differential diagnosis with foreign body aspiration.