We evaluated the long-term clinical results and the survival of the prostheses in eighty-two patients who had had a limb-sparing procedure by means of the implantation of a large-segment prosthesis. All patients had had a high-grade bone sarcoma of the distal, middle, or proximal part of the femur; the proximal part of the humerus; the proximal part of the tibia; or the pelvis. The duration of follow-up ranged from two to twelve years (median, three and one-half years). Function was evaluated with the revised 30-point classification system of the Musculoskeletal Tumor Society. The survival of the prostheses was analyzed with regard to several variables with use of Kaplan-Meier survival estimates. Sixty-eight patients were alive at the latest follow-up evaluation. The survival rate of the prostheses was 83 per cent at five years and 67 per cent at ten years. Twelve prostheses were revised, and eleven revisions were successful. The rate of revision was highest (six of thirteen) in the patients who had had a tumor of the proximal part of the tibia. In contrast, only three (10 per cent) of the thirty-one patients who had had a tumor of the distal part of the femur and three (10 per cent) of the twenty-nine who had had a tumor of the proximal part of the humerus had a revision. Eleven patients (13 per cent) had an infection, which necessitated an amputation in six. Five patients (6 per cent) had a local recurrence, and nine patients (11 per cent), including the six already mentioned, ultimately needed an amputation. Patients who had had a tumor of the proximal part of the humerus had the highest functional scores, while those who had had a tumor of the proximal part of the tibia had the lowest scores. Large-segment prostheses were a good reconstructive option for the treatment of high-grade bone sarcomas in our patients. The rates of long-term survival of the prostheses were acceptable and the functional results were good or excellent after this form of treatment at most of the anatomical sites at which they were used.