Uterine leiomyosarcoma is an uncommon malignancy accounting for approximately 1% of gynecologic oncology cases. Most uterine leiomyosarcomas occur in menopausal women and they are notorious for their aggressive character, early dissemination, and poor prognosis. It is difficult to accurately differentiate uterine leiomyosarcoma from leiomyomas, especially when leiomyomas undergo degenerative changes. We treated two menopausal women with a uterine mass showing cystic change. Clinical work-up included needle aspiration, sonography, computed tomography, and serum tumor markers to differentiate uterine leiomyosarcoma from leiomyoma. All results were negative for malignancy, but uterine leiomyosarcoma was ultimately diagnosed by pathological examination. Until an accurate preoperative diagnostic method is available, menopausal women diagnosed with a degenerating cystic uterine fibroid should be considered to have a malignancy intraoperatively in order to prevent tumor cells from intraperitoneal spreading.