Cotyledonoid dissecting leiomyoma is a benign smooth muscle neoplasm with an unusual growth pattern that is characterized by intramural dissection within the uterine corpus and often a placental-like appearance macroscopically in its extrauterine component that may be alarming to the surgeon. All cases reported to date have been nonaggressive. We report a case in a 33-yr-old woman who had a history of prolonged uterine bleeding. She was operated upon for uterine leiomyomas, and the diagnosis of cotyledonoid dissecting leiomyoma was made at the time of intraoperative consultation. To maintain fertility, the intrauterine tumor was resected by myomectomy and the extrauterine tumor by excision. However, persistent uterine bleeding that eventually became intractable and continued growth of the neoplasm in the uterus necessitated hysterectomy 5 yr later. She was living and well 2.5 yr after hysterectomy with no evidence of disease.