Malignant transformation of multiple chondromas observed in Ollier's disease is a well known possibility. In the clinical case of a 52 year old woman reported here, the sarcomatous transformation of two endochondromatous foci occurred successively in less than one year. One was located in the calcaneus, the other within the proximal metaphysis of the ipsilateral fibula. This case is worth reporting for two reasons: the successive occurrence of these sarcomatous lesions led to a amputation below the knee, later completed by an extended radical resection of the fibula. This combination allowed to preserve the knee with a good functional result and without local recurrence, this clinical case may be compared with that reported by Goodman in 1984. Both cases show that sarcomatous transformations may occur almost simultaneously after a long quiscent period and suggest the existence of a factor that could trigger or favor a malignant transformation process.