Sarcomatous degeneration is one of the serious and rare complications of Paget’s disease of bone. Osteosarcoma is the most common secondary tumour, while other variants such as chondrosarcoma are extremely uncommon. We describe a unique case of Paget’s chondrosarcoma of the pelvis in an elderly female patient, with no previous established diagnosis of osteitis deformans. We emphasize clinical and radiologic aspects that should raise suspicion of malignant transformation, revealing good correlation with the final histopathological diagnosis.