Transformed sarcomas rarely arise from bone infarct lesions, although the majority of bone sarcomas are primary in origin. However, the pathogenesis of the condition is unknown. In this report, we describe a malignant fibrous histiocytoma with a p53 gene mutation. A 59-year-old woman complained of having pain in her left knee for three months. Plain radiographs of the distal metaphysis of her left femur revealed an ill-defined lytic lesion, which was consistent with a malignant tumor in the infarct lesion. An open biopsy specimen did not show any evidence of malignancy. Immunohistochemical examination of the biopsy specimen failed to show p53 protein-positive cells. However, a mutation in the p53 gene was detected when polymerase chain reaction/single-strand conformation polymorphism (PCR-SSCP) analysis was performed. A functionally relevant p53 missense mutation in codon 273 of exon 8 [CGT (Arg) -> CAT (His)] was confirmed by direct sequencing. We concluded that this lesion was a malignant bone tumor arising from the bone infarct lesion, and we thus performed a wide resection. The histopathological diagnosis of the resected specimen was that it was a malignant fibrous histiocytoma associated with bone infarction. Immunohistochemistry revealed that the tumor cells were positive for the p53 protein. To our knowledge, our patient is the first patient having a bone infarct-associated sarcoma with a p53 gene mutation. Identification of the p53 mutation helps in diagnosing the malignant transformation of the bone infarct lesion. One pathogenesis of this condition may be a mutation in the p53 gene.