A 66-year-old man presented with a retroperitoneal mass found in a routine medical examination. He had no complaints and no medical history. Computed tomography (CT) and magnetic resonance imaging (MRI) showed a cystic mass in the retroperitoneal space, attached to the left crus of the diaphragm, 5.5 cm in size. Retroperitoneal cystic tumor was diagnosed, and transperitoneal tumor resection was performed. Pathological findings revealed a cyst wall lined with ciliated epithelium and cartilage, diagnosed as a retroperitoneal bronchogenic cyst. The patient was in good health at 12 months after the surgery with no evidence of recurrence.