OBJECTIVE: To compare whole-body MRI (WB-MRI) with clinical examination in the assessment of disease activity in juvenile dermatomyositis (JDM). METHODS: Whole-body MRI was obtained in 41 patients with JDM and 41 controls using a 1.5T MRI scanner and short τ inversion recovery sequences, and 18 patients were followed up with WB-MRI examinations. Abnormal muscle, subcutaneous tissue, and myofascial signals were scored according to 36 muscle groups and proximal and distal involvement of the extremities. WB-MRI and clinical evaluation were performed simultaneously and the results were compared. Validation procedures included analysis of plausibility and reliability, structural validity, screening power, and responsiveness. Results: WB-MRI identified muscle inflammatory infiltrates in the distal leg (26/41 patients) and forearm (19/41 patients) that were not detected by clinical examination, while WB-MRI was able to accurately assess subcutaneous (23/41 patients) and myofascial (13/41 patients) involvement. 27 patients showed patchy distribution of muscle inflammatory responses in areas of abnormal muscle high signal, however, 7 patients showed a homogeneous distribution of this abnormal signal. The results of WB-MRI scoring of muscle, subcutaneous tissue and myofascia were excellent. there was a good correlation between WB-MRI muscle scores and disease activity (muscle strength test: rs = -0.84, pediatric myositis assessment criteria: rs = -0.81). Compared to controls and patients with inactive juvenile dermatomyositis , patients with active juvenile dermatomyositis had higher WB-MRI scores (Pb<0.0001) along with better responsiveness (standardized response mean = 1.65). Nine of the follow-up WB-MRI patients demonstrated remission of inflammation, whereas only five patients met the criteria for clinical remission, as judged by clinical criteria. CONCLUSION: WB-MRI provides additional information for the clinical evaluation of patients with juvenile dermatomyositis and is expected to be a powerful tool for assessing the overall inflammatory response in juvenile dermatomyositis, developing individualized treatment plans, and monitoring treatment efficacy.