The malignant transformation of a uterine leiomyoma is still debated and, if it occurs, it is very rare. The case of a patient affected by three small leiomyomas, monitored by the same gynecologist over the years is described. Two of these leiomyomas were transformed into leiomyosarcoma after menopause and the patient died despite receiving therapy. The case reported here is meant to underline the need to keep all uterine myomas in check since the transition into leiomyosarcomas may occur with an evolution over a time period which has not been established so far.