Bronchogenic cysts are benign lesions, which are usually described at the chest level. We present here a case report of a retroperitoneal bronchogenic cyst. A 77-year-old man presented with a left retroperitoneal tumor discovered by scanner. There was no endocrine disruption. Excision of the lesion was performed and final diagnosis was a bronchogenic cyst. Current widespread use of modern radiology enables increased discovery of such "incidentalomes". In the future, pathologists will be routinely faced with this type of diagnosis, which up to now has been described as exceptional.