We report a case of recurring femoral hydatid disease in a trisomic-21 patient 5 years after a primary surgery. The patient presented a thigh abscess with a lateral supracondylar area fistula. The workup demonstrated massive osteolysis involving the proximal, diaphyseal, and distal femur as well as multiple soft tissue cystic masses but no metastases. Treatment consisted in cystic masses debridment, extensive bony-curettage of the intraosseous cystic zones, temporary weight-bearing suppression, and albendazole. The patient remains under follow-up and cannot be considered definitely cured.