Cystic hygroma is a benign tumor of lymphatic origin encountering most frequently in young children, and composed of softly fluctuated mono or multilocular cystic masses which developed from embryonic outpouching of the venous system. The majority of these tumors are found at the anterolateral neck region particularly posterior .triangle, and occasionaly axilla, mesentery and spleen etc. In the mediastinum, the incidence of hygroma is very rare and also of mediastinal neoplasms. Recently, we have experienced 2 cases of mediastinal cystic hygroma connected up lateral neck and to anterior chest wall respectively, which were surgically removed successfully and confirmed histopathologically. Authors present the cases and discussion with a brief review of the relevant literatures.[KTCS 1977;1:65-70]