Clinical MRI of patients with juvenile osteochondritis dissecans (JOCD) relies on morphological, spin echo imaging with long echo times that cannot unambiguously distinguish between the cartilaginous, fibrous and osseous tissues within lesions. This 3T study evaluates 34 JOCD lesions from 25 patients using morphological MRI and T2* mapping. JOCD progression was associated with a significant T2* decrease in progeny and interface. Additionally, significantly lower T2* in stage IV progeny and parent bone of stable lesions suggests increased bone density compared to the healthy, control bone. T2* mapping provides quantitative evidence of disease progression which may help inform clinical JOCD management.