In Legg-Calvé-Perthes disease (LCPD), magnetic resonance imaging (MRI) and conventional radiography in two planes are considered the most important methods of investigation for early diagnosis and for assessment of the course of the disease. MRI can reveal the early marrow oedema, thus allowing early differential diagnosis against diseases that are similar in clinical appearance (coxitis fugax, epiphyseal dysplasia). The extent of the necrotic area within the epiphysis, the most important indicator of the prognosis of the disease and thus for the therapeutic management, can be assessed earlier and more reliably with MRI than with other techniques. The loss of containment can be visualized by MRI, because depiction of the cartilaginous structures is possible earlier than with conventional radiography. Staging of LCPD is also possible with MRI, especially in stages I and II. Radiography shows the reossification and the osseous remodelling of the epiphysis better. A disadvantage of MRI seems to be the occasional need for sedation or anaesthesia of the child to avoid motion artefacts.