Twenty-three children with Legg-Calvé-Perthes disease were examined to determine the femoral head shape. We evaluated and correlated conventional radiography, arthrography and MR imaging. In the a.p. view, measurements were obtained from the center of the femoral head along the bony or cartilaginous outline at 30 degrees intervals. Maximum flattening of the cartilaginous outline appeared laterally, 60 degrees from the center of the baseline of the epiphyseal index and the caput index. Maximum flattening of the bony outline was found at 75 degrees. Arthrography and MR imaging gave the same information about the shape of the femoral head cartilage. The bony femoral head shape on conventional radiographs in the a.p. view did not reflect the cartilage shape obtained by MR and arthrography.