BACKGROUND: Legg-Calve-Perthes disease (LCP) is necrosis of the proximal femoral epiphysis of vascular origin. Clinical course and outcome in LCP disease varies considerably between different patients. Earlier prognostic criteria than those offered by conventional radiography are necessary to identify children who require prompt surgical treatment. OBJECTIVE: To assess the significance of signal alteration on diffusion-weighted MR imaging (DWI MR) in LCP. MATERIALS AND METHODS: Twelve boys with unilateral LCP disease (Catterall grade 2 and 3), at the initial sclerotic stage and early fragmentation phase, underwent dynamic gadolinium-enhanced subtracted (DGS) and DWI MR. For DGS MR, the lateral pillar enhancement was recorded. For DWI imaging, we measured ADC values in the diseased and the unaffected epiphyses and metaphyses. Receiver operating characteristic curves were performed to analyze the performance of DWI in establishing agreement with the results of DGS MR, which is the gold standard for prognosis. RESULTS: Femoral epiphysis increased diffusivity was observed in the affected hip in all cases. Increased metaphysis diffusivity in the affected side was observed in all cases with absent lateral pillar enhancement at DGS MR. CONCLUSION: DWI seems to be a noninvasive means of distinguishing between Perthes disease with favourable and unfavourable prognosis.