Since the first description of osteochondritis dissecans, there has been an unfortunate tendency in the scientific literature to include all age groups, whether the epiphysis is closed or open, in the same article. Juvenile osteochondritis dissecans (JOCD) is distinct from osteochondritis dissecans (OCD), which occurs after the femoral epiphysis is closed. JOCD is not a osteochondral fracture, an accessory center of ossification, hereditary dysplasia, or osteonecrosis. JOCD has a vastly more favorable prognosis than does OCD and, by definition, presents prior to the closing of the adjacent epiphysis. The etiology of JOCD is a stress failure syndrome of subchondral bone, related to a cumulative exercise dose administered over months or years to the immature knee. The goal of treatment of JOCD is to obtain healing of the lesion prior to closing of the epiphysis, when the prognosis becomes poor. In most cases, this healing can be obtained by activity restriction alone. When this is not successful, aggressive steps must be taken to promote lesion healing. Preservation of joint surface congruity and orthopticity must be perfect to avoid the inexorable arthrosis if treatment fails.