We describe the case of a 24-year-old woman with a giant cell tumor originating from the distal part of the sacrum, which was almost completely filling the pelvis and extending to the umbilicus. At laparotomy, the tumor was separated from all of the pelvic structures including the ureters. The sigmoid colon was transected and the tumor was dissected down to the pelvic floor. A separate perineal incision was made, the rectovaginal septum was entered, and the posterior vaginal wall was bisected to give better access. It was possible to mobilize the tumor completely after dividing the rectum 5 cm from the anus. All macroscopic tumor was removed in continuity with the sigmoid colon. The ovaries were transposed to the paracolic gutter to avoid artificial menopause following radiation therapy. A sigmoid colostomy was formed. Because histology could not provide definite evidence of complete removal of the tumor, radiation therapy to the sacrum was given. Forty-two months after her surgery, the woman remains free of disease. The abdominoperineal approach should be considered for patients with a large tumor which is fixed to the sacrum.