Juvenile osteochondritis dissecans (JOCD) lesions contain cartilaginous, fibrous and osseous tissues which are difficult to distinguish with clinical, morphological magnetic resonance imaging (MRI). Quantitative T₂^** mapping has earlier been used to evaluate microstructure and composition of all aforementioned tissues as well as bone mineral density. However, the ability of T₂^** mapping to detect changes in tissue composition between different JOCD lesion regions, different disease stages, and between stable and unstable lesions has not been demonstrated. T₂^*his study analyzed morphological and T₂^** MRI data from 25 patients (median age, 12.1 years) with 34 JOCD-affected and 13 healthy knees. Each lesion was assigned a stage reflecting the natural history of JOCD, with stages I and IV representing early and healed lesion, respectively. T₂^** values were evaluated within the progeny lesion, interface and parent bone of each lesion and in the control bone region. T₂^** was negatively correlated with JOCD stage in progeny lesion (ρ = −0.871;​ p < 0.001) and interface regions (ρ = −0.649;​ p < 0.001). Stage IV progeny showed significantly lower T₂^** than control bone (p = 0.028). T₂^** was significantly lower in parent bone than in control bone of patients with stable lesions (p = 0.009), but not in patients with unstable lesions (p = 0.14). Clinical significance:​ T₂^** mapping enables differentiation between different stages of JOCD and quantitative measurement of the ossification degree in progeny lesion and interface. T₂^*he observed T₂^** decrease in healed and stable lesions may indicate increased bone density as a result of the active repair process. T₂^** mapping provides quantitative information about JOCD lesion composition.