Osteochondritis dissecans (OCD) is an acquired idiopathic lesion of subchondral bone that can produce delamination and sequestration with or without articular cartilage involvement and instability. The cause of OCD is still debated: the most recognized etiology is the occurrence of repetitive micro-traumas associated with vascular impairment, causing progressive ankle pain and dysfunction in skeletally immature and young adult patients. Ankle OCD is classically located in the medial part of the talus, while lateral and posterior involvement is less frequent. Diagnosis of OCD, based on MRI findings, is quite straightforward; MRI examination can also be very useful for dating the defect and obtaining information about the associated bone bruise. Osteochondritis dissecans, if not recognized and treated appropriately, may lead to secondary osteoarthritis with pain and functional limitation. Surgical treatment is mandatory especially in young patients with unstable cartilage fragments. There are various surgical options: fixation, microfracture, or substitution using autologous chondrocyte implantation techniques.