We experienced 8 cases of esophageal cysts on between January, 1965 and March, 1989. During the same period, 320 cases of mediastinal tumors were operated in our department, and esophageal cysts were 2.5% of these cases. They were 7 males and 1 female, and ranged in age from 5 to 51 (mean 29.9) years. The cysts were located in the right in 6 and in the left in 2, and in the upper third of the esophagus in 1, middle third in 3 and lower third in 2 cases. A correct preoperative diagnosis was made in only 1 case. The definite diagnoses were not obtained from thoracic CT scans and esophagography. We tried transesophageal ultrasonic endoscopy in the recent 2 cases, and could diagnosed in 1 case as a cyst in the esophageal wall. The another case, we could not diagnose, was a cyst attached to the esophageal wall by a muscular stalk. We experienced 2 cases of post operative bleedings, so we must be careful of hemostasis of the muscular layers after enucleation of the cysts. Histological examinations of the cysts showed ciliated columnar epithelium in all cases. Cartilage were observed (bronchogenic cysts) in 4 patients (50%) and two muscle layers were observed (duplication cysts) in 4 other patients (50%). But 2 cases of bronchogenic cysts had two muscular layers, 1 case of them was well-defined. And 1 case of duplication cyst had poor two muscular layers. We cannot divide clearly the esophageal cysts into bronchogenic cyst or duplication cyst, in the point of having cartilage and double muscle layers.(ABSTRACT TRUNCATED AT 250 WORDS)