Cystic lymphangioma of the mediastinum (CLM) is extremely rare, usually a lot of the patients were found to have the disease by accident in adulthood.It is difficult to be diagnosed but surgery.We have received and treated a case and the diagnosis and therapy are worth discussing. Cystic lymphangioma of the mediastinum (CLM) is extremely rare, usually a lot of the patients were found to have the disease by accident in adulthood. It is difficult to be diagnosed but surgery. We have received and treated a case and the diagnosis and therapy are worth discussing