The patient was a 59-year-old woman in whom computed tomography revealed a posterior mediastinal cyst and ovarian cystoma at a medical check-up in March 2007. Blood tests showed high CA19-9 and CA125 levels. She underwent left adnexectomy for ovarian cystoma in July 2008 and histopathological examination led to a diagnosis of dermoid cyst. The postoperative levels of CA19-9 and CA125 remained high. She developed dysphagia in February 2009, and the posterior mediastinal cyst showed a tendency to enlarge. Therefore, she underwent tumorectomy through a small thoracotomy. The cyst contained greenish fluid with CA19-9 and CA125 contents of 65,000 and 78,000 U/ml, respectively. Histologically, the cyst had a thickened wall, which contained two muscle layers, and was lined by squamous and pseudostratified ciliated epithelium. No cartilage or bronchial glands were identified. These findings led to a diagnosis of esophageal cyst. On immunohistochemical staining, the cyst-lining epithelial cells were positive for CA19-9 and CA125. The serum CA19-9 and CA125 levels returned to normal two months after surgery. We report a resected case of esophageal cyst producing CA19-9 and CA125.