Abstract Hydatid cystic disease is a significant clinical problem in endemic countries. Hydatid cysts are most commonly located in the liver and lungs. Primary mediastinal hydatid cyst is a rare clinical entity. The diagnosis must be considered in a patient with a mediastinal mass, particularly in endemic regions. Mediastinal hydatid cysts causing paralysis of phrenic and recurrent laryngeal nerves have been rarely reported. We describe a rare case of primary mediastinal hydatid cyst associated with diaphragmatic palsy caused by compression of the left phrenic nerve, which was successfully treated with partial cystectomy and capitonnage with hemidiaphragmatic plication.