Purpose: Previous studies reported variable outcome and failure rates after mega-prosthetic reconstructions in the lower extremities. The purpose of this study was to make a long-term single-center evaluation of patients treated with limb-sparing surgery and reconstruction with mega-prostheses in the lower extremities. Methods: We identified 50 patients (osteosarcoma (n = 30), chondrosarcoma (n = 9), osteoclastoma (n = 6), Ewing sarcoma (n = 4), angiosarcoma (n = 1)), who underwent limb-sparing reconstruction of the lower extremities (proximal femur (n = 9), distal femur (n = 29), proximal tibia (n = 9), and the entire femur (n = 3)) between 1985 and 2005. Surviving patients not lost to follow-up were evaluated using the MSTS score. Causes of failure were classified according to the Henderson classification. Kaplan-Meier survival analysis was used for evaluation of patient, prosthesis, and limb survival. Results: Twenty-eight patients were alive at follow-up. Fifty-four percent had revision surgery (n = 27). The ten year patient survival was 60% (95%CI 46–74%); the ten year implant survival was 24% (95%CI 9–41%), and the ten year limb survival rate was 83% (95%CI 65–96%). Type 1 failure occurred in 9%, type 2 in 16%, type 3 in 28%, type 4 in 18%, and type 5 in 3%. Mean MSTS score was 21 (range, 6–30), representing a median score of 71%. Conclusions: Our long-term results with mega-prostheses justify the use of limb-salvage surgery and prosthetic reconstruction. Our results are fully comparable with other findings, with regard to limb and prosthesis survival, but also with regard to functional outcome.