Chief complaint, medical history Patient, female, 35 years old, was admitted for “finding a right lower abdominal mass for 4 months.” She was admitted to the hospital and underwent a subtotal hysterectomy for uterine smooth muscle tumor in 2008 and a repeat pelvic mass resection + partial cystectomy + tipped tissue flap transplantation for pelvic smooth muscle sarcoma in 2014. A right lower abdominal mass was found again 4 months ago. Examination and ancillary CT examination showed a huge right-sided mid-lower abdominal pelvic mass with a size of about 19.5 cm × 14.1 cm × 7.5 cm, and a slightly high-density shadow was seen within the line, and enhancement was seen with heterogeneous enhancement and bladder compression; malignant tumor was considered. Diagnosis and management After perfecting the relevant preoperative examination, a dissection and resection of the huge pelvic mass was performed under general anesthesia in May 2015, and the mass was successfully and completely removed without damaging the surrounding tissues and organs. The excised mass was sent to pathology, and the later return showed: smooth muscle sarcoma, which was considered as uterine smooth muscle sarcoma in combination with medical history. He recovered well after surgery and was discharged 10 days after surgery, and is under regular follow-up. Follow-up and discussion Smooth muscle sarcoma is a very aggressive malignant tumor, prone to distant metastasis and recurrence, and even with early diagnosis, the recurrence rate still reaches 53%-71%. It is characterized by rapid growth within a short period of time, and the volume of smooth muscle sarcoma can increase about 1 times within 3-6 months. The overall survival rate varies from 15% to 25%, with studies showing an average survival of only 10 months. The prognosis is extremely poor. Surgery is the main treatment method and is not sensitive to radiotherapy and chemotherapy. The age of the tumor patient, the stage, grading and size of the tumor are factors that affect the prognosis.