Hydatid disease is caused by the larval stages of a cestodes belonging to the genus Echinococcus. In humans, hydatid larva and cysts are located >90% in the liver and/or lungs. Primary mediastinal location, with absence of documented lung infection, is extremely rare and has not been previously reported in Chile. We report the first case of a primary mediastinal hydatid cyst in Chile and review the literature. A 38 year old woman was admitted because of a painful right supraclavicular mass, dyspnea on exertion and logical dysphagia. Presurgical evaluation evidenced a mediastinal tumor extending to the cervical region that was successfully removed. The diagnosis of mediastinal hydatid cyst was confirmed macroscopically and by biopsy.