Background: Broad ligament leiomyoma is the most common extrauterine leiomyoma, but with a very low incidence rate. When broad ligament leiomyoma is giant and undergoes degeneration, it poses both clinical evaluation and radiological difficulty in differentiating from an ovarian tumor. Meanwhile the changes of anatomical structure increased the difficulty during surgery. Conclusions: Thus, the diagnosis of a cyst-solid complex adnexal mass with a marginally raised serum level of CA125 might be a broad ligament leiomyoma with degeneration besides a ovary tumor. During surgery of myomectomy, we should be meticulous hemostasis and avoid ureter and bladder injury and other complications.