The authors postulated that there may be differences structurally of Leeg-Perthes' disease from those of normal hips. In this connection, we measured various X-ray indices of healthy side hips (56 cases) of unilaterally involved Legg-Perthes' disease and of equal number of hips from Legg-Perthes' unrelated disease children. The comparison between those two groups have been made and may be summarized as follws;1. The criteria of judgement were epiphyseal index, C-E angle, migration of femoral head, sphericity of the femoral head by Mose's concept, and medial joint space. 2. In Legg-Perthes disease patients, the average epiphyseal index was 0.43±0.091, C-E angle 23.0±4.64, migration index, 0.16±0,079 medial joint space 8.4±1.84mm, for the control group 0.50±0.050, 24.1±4.96, 0.15±0.045, 8.1±1.51 mm in order respectively. 3. Regarding to sphericity of femoral head according to Mose's concept in Legg-Perthes disease patient, there were 6 cases which showed difference more than 2mm in their sphericity. In control group, none had over 2 mm out of 56 cases. 4. There were significant differences statistically, in epiphyseal index and head sphericity, which revealed the structural differnce rather than femoral head containment difference between the two groups.