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The giant cell tumor of bone (GCT) represents 18 % of benign bone tumors but it's unpredictable, aggressive behavior, it's tendency to recur locally, develop "benign" pulmonary metastases, and become malignant has caused a grate debate and confusion about it's nature. The occurrence of more than one lesion (multicentric GCT) and malignant transformation without previous radiotherapy are exceedingly rare. We report a case of a patient that developed a secondary malignant transformation 13 years after a surgery for a lesion in distal tibia initially interpreted as an aneurysmal bone cyst. It recurrs locally after ten years period of latency. A third recurrence demonstrated the histological features of GCT. More later, a second lesion in distal fibula developed. Further, it extends into soft tissue and is detected a sarcomatous transformation. Pulmonary metastases are observed. We concluded that our patient have a secondary malignant transformation because a sarcoma developed in the same site of a previous GCT.