Background The extension of hydatid liver cysts into the mediastinum through diaphragmatic hiatus is extremely rare. In this report, we describe a rare case of a hydatid liver cyst with mediastinal extension through Larrey’s hiatus, emphasizing the surgical strategy for successful treatment. In this report, we present the first documented case of a hydatid liver cyst extending into the mediastinum through Larrey’s hiatus. Case presentation We report the case of a 65-year-old male who presented with right-upper-quadrant and left-sided chest pain evolving for two months. Physical examination showed dullnes in the epigastric region. A thoraco-abdominal CT scan, revealed a 13 cm mediastino-abdominal hydatid cyst, centered on the left liver lobe with extension into the mediastinum through the Larray’s diaphragmatic hiatus. The patient underwent surgical management. Both thoracic and visceral surgeons were involved. The surgical management involved both thoracic and visceral surgeons. A Makuuchi incision allowed resection of the hydatid liver cyst. The mediastinal portion of the cyst, resting on the pericardium was aspirated through Larrey’s hiatus, followed by irrigation with a scolicidal solution. The postoperative course was uneventful. Conclusion Transmediastinal hydatid liver cysts are rare and should be operated on in close collaboration between visceral and thoracic surgeons to prevent complications.