Background. We report a case in which tracheal stenosis and granulomatous polyp were managed through appropriate treatment of Kommerell's diverticulum. Case. A 76-year-old man had undergone total arch replacement and thoracic endovascular aortic repair (TEVAR) for a Kommerell's diverticulum in 2015. He experienced respiratory difficulty in 2017. As his symptoms did not improve, he underwent chest computed tomography (CT) and bronchoscopy; the patient was then transferred to our department and hospitalized owing to suspicions of a tracheal tumor. Considering the possibility of tracheal stenosis due to the enlargement of Kommerell's diverticulum resulting from an endoleak, the patient underwent a second TEVAR. Bronchoscopic biopsy was performed after total interruption of blood flow into the Kommerell's diverticulum. A polyp-like lesion was identified in the lower trachea; histopathological examination revealed a granulated tissue lesion. Extubation was performed on postoperative day 3, after which improvement was noted in the tracheal stenosis caused by the granulomatous polyp. The granulomatous polyp improved by tracheal tube compression and biopsy. CT and bronchoscopy performed 2 months postoperatively revealed no tracheal stenosis caused by compression of the Kommerell's diverticulum. Conclusions. Kommerell's diverticulum is an extremely rare condition characterized by an abnormal protrusion in the left subclavian artery with localized cystic dilatation. As the enlargement of a Kommerell's diverticulum can result in severe tracheal stenosis, determining the appropriate treatment strategy is of paramount importance.