Mesothelial cysts have many other names, such as pericardial celomic cyst, pleura- diaphragmatic cyst, simple cyst of the mediastinum, springwater cyst, serosal cyst, etc. (Petereit 1972, Drash 1950). Most mesothelial cysts are believed to originate from malformations of the pericardium, but some, like the one in this case, are believed to result from a pleural malformation. (Ochsner 1966, Lambert 1940). Mesothelial cysts are extremely rare and can be confirmed histologically by special stains. A 64 year old woman was admitted due to a painless bulging mass in her right neck. The operation was performed with the initial diagnosis of cystic lymphangioma confirmed by computer tomography and total excision was possible. The diagnosis of mesothelial cyst of the mediastinum was confirmed by histologic examinations (stainings) and the patient was discharged from the hospital without any significant complications.