We report a very rare case of primary mediastinal hydatid cyst which invaded the ascending aorta and the aortic arch which initially presented as a cranial mass. Aortic wait is a very unusual site for the hydatid cysts. To the best of our knowledge, this is the first reported case of hydatid cyst located within the aortic arch turner. Patient underwent ascending aortic and hemiarch replacement under hypothermic circulatory arrest and removal of the cyst. Patient had an uneventful recovery and has been on follow-up. Although the literature data are very limited, we believe that the aortic procedure of choice should be graft interpositon rather than patch repair. (c) 2007 European Association for Cardio-Thoracic Surgery. Published by Elsevier B.V. All rights reserved.