We report the case of a retroperitoneal hydatid cyst ruptured into the infrarenal abdominal aorta. Initial treatment consisted of marsupialization of the cyst with patch angioplasty of the aorta. Formation of a false aneurysm led to reoperation for placement of an aortobifemoral bypass, but the patient died postoperatively. In spite of the exceptional character of this location, diagnosis should be suggested routinely in endemic areas when a retroperitoneal mass is discovered. Treatment should be either in situ prosthetic replacement or extra-anatomic exclusion bypass.