Background: Bronchogenic cysts are developmental abnormalities of the primitive foregut which typically occur in the lung. Subdiaphragmatic and, especially, retroperitoneal locations are rare. The histopathological definition consists of the presence of ciliated epithelium together with cartilage or bronchial Mucous glands. Case presentation: We report on a 49-year-old patient with the incidental finding of a large cystic mass between the diaphragm and the stomach. Imaging studies suggested an adrenal tumour. Surgical resection and postoperative follow-up were uneventful. Histological examination revealed the surprising diagnosis of a bronchogenic cyst. Conclusion: Bronchogenic cysts must be considered in the differential diagnosis of retroperitoneal cystic lesions. Regardless of being asymptomatic most of the time, surgical resection is recommended to obtain definitive histological diagnosis and avoid future complications.