A case is presented of a 55-year-old man with a MFH in a previous BI. The poor prognosis of such secondary MFH is related in part to the difficulty of its early diagnosis, its aggressive behavior, and its tendency to metastasize (mainly to bone sites and lungs). Nevertheless, although biopsy of asymptomatic bone marrow infarction is not indicated, MRI seems consistent in detecting sarcomatous transformation of symptomatic BIs and plays an important role in the patient's preoperative evaluation.