A 4-year-old girl with a presacral benign mesenchymoma is reported. The nature of the tumor was not recognized preoperatively or intraoperatively. There was evidence of pericapsular infiltration of the soft tissues of the pelvis but not signs of malignancy. A follow-up examination after 3 months indicates that the patient has no clinical evidence of recurrence. Review of the English literature shows the rarity of benign mesenchymoma in childhood and the lack of reports of its occurrence in the pelvis.