Objective: Smooth muscle tumor of uncertain malignant potential (STUMP) shares some characteristics with sarcoma but does not meet the full diagnostic criteria. Morcellation is a technique used to extract surgical specimens through a small incision, thereby spreading unsuspected malignant cells. We report a case of STUMP that recurred postoperatively in the abdominal cavity. Case Report: Surgery was performed on a patient diagnosed with uterine leiomyoma, with the tumor morcellated transvaginally. Twelve months later, several abdominal tumors appeared. Pathological specimens were reevaluated, and STUMP was diagnosed. Many tumors in the abdominal cavity of the patient were removed surgically. The postoperative pathologic diagnosis was leiomyosarcoma. Conclusion: This case of unsuspected STUMP recurrence after transvaginal scalpel morcellation illustrates the risk of spillage of malignant cells. Surgeons and surgical pathologists must stay alert to the possibility of occult malignancy, and morcellated tissues should be carefully examined.