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Esophageal duplication cysts are enteric-induced congenital anomalies and they are very rare in the anterior intestine cysts. Symptomatic cases are detected at an early age, and in asymptomatic patients, the diagnosis is usually in the thirties or the 40s. The patient was admitted to the center due to upper respiratory tract infection and the chest X-ray revealed a paravertebral opacity in the right hemithorax. Thorax CT and PET-CT were taken to the patient. In PET-CT there was a 43x27.4 mm lesion in upper segment of the right lung lower lobe, located in Th-6-7-8 paravertebral area. There was a hypointense hypometabolic cyst with midline calcifications of the corpus of the adjacent vertebrae. Duplication cyst was excised by right posterolateral thoracotomy. After pathological examination, the diagnosis of esophageal duplication cyst was confirmed histopathologically. Mediastinal foregut cyst should be considered in the differential diagnosis in all patients with mediastinal mass on chest X-ray. Complications and malignant degeneration can be prevented by early surgical resection.