The treatment of deep chondral defects at the knee joint poses major difficulties and challenges to the orthopaedic surgeon, particularly in young patients for whom solutions like total or hemi-joint arthroplasty are not recommended, because of their limited durability. Biological resurfacing with materials such as perichondrium, periosteal allografts, and cultured chondrocytes is still at the experimental stage and there has been limited clinical validation. Since 1978, we have successfully used fresh osteochondral ('shell') allografts for the treatment of selected patients with a chondral defect at the knee joint. These grafts, implanted mainly in young patients, have proved durable and have provided good functional results for more than 15 years, as shown by an average of 84.6 in the Hospital for Special Surgery (HSS) Knee Score. The operative technique and results of long-term follow-up of patients receiving fresh, osteochondral ('shell') allografts are presented and discussed.