Background: The present study was performed to determine whether there is a difference, with regard to functional outcome and quality of life, between endoprosthetic replacement and rotationplasty for the treatment of malignant tumors of the distal part of the femur or the proximal part of the tibia.Methods: Sixty-seven patients, between the ages of eleven and twenty-four years at the time of the diagnosis, had a malignant tumor of the distal part of the femur or the proximal part of the tibia. A rotationplasty was performed in thirty-three patients, and an endoprosthetic replacement was done in thirty-four patients. The median duration of follow-up was six years and one month (range, two years to sixteen years and two months). The scale developed by the Musculoskeletal Tumor Society was used to evaluate the functional results. Quality-of-life issues were assessed with the questionnaire developed by the European Organization for Research and Treatment of Cancer.Results: The patients who had had a rotationplasty had a mean functional score, according to the system of the Musculoskeletal Tumor Society, of 24 points, and the patients who had had an endoprosthetic replacement had a mean score of 25 points. This difference was not found to be significant, with the numbers available (p = 0.47). Only one patient who had had a rotationplasty used an assistive device when walking long distances, whereas six patients who had had an endoprosthetic replacement used an assistive device. This difference was significant (p < 0.001). The quality-of-life questionnaire revealed that the patients who had had a rotationplasty could participate in hobbies such as carpentry and sports as well as in other daily activities to a significantly greater degree than those who had had an endoprosthetic replacement (p = 0.001). Restriction in daily activities due to pain was significantly less common in the group that had had a rotationplasty than it was in the group that had had an endoprosthetic replacement (p = 0.047).Conclusions: Rotationplasty was not associated with any disadvantages with regard to function or quality of life in comparison with endoprosthetic replacement. It is possible that the psychosocial outcome is influenced by the fact that patients who have a rotationplasty know that additional operative intervention is not usually necessary. Despite good functional and quality-of-life results, the cosmetic appearance may be the most serious disadvantage of rotationplasty. The decision to perform this procedure must be made on a case-by-case basis.