Background: Giant cell tumor (GCT) of the feet is rare and occurs in less than 1% of all GCTs of the extremities. Some may have a secondary formation of an aneurysmal bone cyst (ABC). Diagnostics may include radiographs and magnetic resonance imaging (MRI) and treatment varies depending on its classification. Preferably, limb salvage is the treatment of choice. Presentation of Case: We present a 21-year-old male with a large mass in the right heel with pain and difficulty ambulating. The mass involves clinically the whole of calcaneus and is hard, non-tender, non-erythematous, and non-movable. Radiographs show a well-defined osteolytic lesion with a sclerotic rim and neocorticalization. MRI shows fluid-fluid levels. A core needle biopsy was done revealing GCT with secondary ABC. Neoadjuvant therapy using denosumab was given. The patient underwent a marginal excision via total calcanectomy, with reconstruction and subtalar joint arthrodesis using proximal femur allograft secured with 4mm cancellous screws and Achilles tendon V-Y lengthening and reattachment to the allograft via single row suture anchor fixation. At 5 months follow-up, the patient had an excellent clinical appearance with a fused subtalar joint and stable calcaneocuboid joint. Discussion: Intralesional curettage is still the mainstay of treatment when feasible. However, large aggressive lesions may need marginal or wide excision and reconstruction, and in rare cases maybe amputation. We decided to do salvage surgery for the patient and restore as much function as we can. We used the proximal femur allograft as its size and shape are almost the same as with the contralateral calcaneus. Conclusion: Limb salvage surgery, via total calcanectomy and reconstruction using a proximal femur bone allograft, is one good option in treating GTC involving the whole calcaneus. Its main advantage is that the proximal femoral allograft could be fashioned and contoured to be similar in shape and dimensions to the native calcaneus.