We report the case of a 75-year-old woman who developed acute mediastinitis from an infected bronchogenic cyst due to endoscopic ultrasound-guided transesophageal fine-needle aspiration (EUS-FNA) for making diagnosis. The patient developed fever, chest pain, and discomfort after EUS-FNA. A repeat chest computed tomography( CT) demonstrated a rapidly increased size of the mediastinal mass. Thoracoscopic surgery was performed five days after EUS-FNA and the mediastinal mass was excised successfully. Postoperative histological examination confirmed the diagnosis of a bronchogenic cyst.