The presence of a massive full-thickness osteochondral defect in the knee of young and active individuals is an unsolved problem in orthopedic surgery, especially in post-traumatic large bone defects. Fresh massive osteochondral allografts have been used for many years but mostly in oncology but not in post-traumatic cases. This case report describes a 20-year-old right leg-dominant woman, who, at age 19, sustained open Gustilo-Anderson type III comminuted fractures of the left patella and lateral femoral condyle in a motorbike accident. Initial treatment included immediate débridement and patellectomy with lavage. The large defect of the femoral condyle was reconstructed with a massive osteochondral allograft 1 year after the injury. The graft was obtained from our institutional tissue bank. The damaged bearing part of the condyle was resected to bleeding bone to create the nearly rectangular defect. The central condyle wall remained intact. The graft was trimmed to fit the defect and fixed with three cancellous 6.5-mm screws. The meniscus was not damaged. Partial weight bearing was permitted at 8 weeks and full weight bearing at 16 weeks after the surgery. At the last follow-up control 10 years after the surgery, no evidence of tibiofemoral arthrosis was present. The allograft-host interface was not visible. The radiodensity of the graft was nearly identical to the host bone. The Lysholm score and clinical findings were identical (100 points) to those 18 months after the surgery. The patient was extremely satisfied without complaints at 30 years of age.