In a prospective study of 22 patients (24 hips) with Legg-Calvé-Perthes disease (LCPD) the findings at conventional radiography, arthrography, bone scintigraphy and MR imaging, obtained at the time of diagnosis, were compared. MR was superior to conventional radiography and bone scintigraphy in the detection of the extent of involvement in the femoral head. Arthrography was as good as or better than MR imaging in determining the shape of the articular surfaces and the occurrence of lateral subluxation. Conventional radiography was less sensitive in identifying the degree of lateral subluxation and the extent of the necrosis in the femoral head. MR imaging provided anatomical and pathophysiological information about the extent and location of head involvement as well as the degree of lateral subluxation. Revascularisation was more clearly demonstrated with MR than with bone scintigraphy, irrespective of symptom duration.