Osteochondritis dissecans of the knee is diagnosed at an increasing rate among adolescents and young adults. One of the reasons is due to the increasing number of sports participants among these populations. Although many theories exist, the cause of osteochondritis dissecans is unknown. Early diagnosis is very important. While adult type osteochondritis dissecans is unstable, in most young patients it is stable, and patients with an intact articular surface have a good chance to heal with non-operative treatment and cessation of physical activity. The value of complementary treatment (bed rest, partial weight bearing, bracing aimed at reducing weight bearing of the involved knee) is unknown. Patients with open physes and stable lesions, who failed non-operative treatment, may be treated with local bone drilling, encouraging lesion healing. As the disease progresses, more aggressive measures should to be taken, whilst decreasing success ratios are expected. The healing potential of the lesion may be evaluated by magnetic resonance imaging. Most adult type osteochondritis dissecans patients, as most young patients, with unstable lesions and loose bodies within their knees, are treated with fixation of the lesions and even bone grafting. Many unstable lesions will heal after fixation, but the long-term prognosis is elusive. Chronic loose bodies are very difficult to fix, with less favorable outcomes. Excision of large lesions originating from weight bearing cartilage is not favorable and different rehabilitation measures of local cartilage damage are not encouraging.