We performed the magnetic resonance imaging (MRI) study on the 65 hips in 51 children with Legg-Calve-Perthes disease (LCP) at Seoul National University Childrens Hospital from July 1989 to February 1992, with the aim of determining the efficacy of MRI for the assessment of LCP. The average age of the patients was 6.8 years. We compared the results of MRI findings with that of simple roentgenographic and arthrographic findings, and evaluated the results on the basis of five aspects: First, Catterall grouping and lateral pillar grouping according to the stage of the disease; Second, the exact location, shape and contents of the metaphyseal cyst; Third, relationship between the cyst and physis, presence of physeal injury; Fourth, morphological changes of intra-articular structures; Fifth, ossification process of hypertrophic cartilage of femoral head. We obtained following results. 1. The Catterall groups of MRI were higher than those of simple reontgenogram in 15 hips (23%), and the ratio of the higher MRI grouping was greater in early stage of the disease. The lateral pillar groups of MRI were higher than those of simple roentgenogram in 39% of the hips at avascular stage, and in 24% of hips at fragmentation stage. 2. In 25 hips, the exact locations and shapes of the metaphyseal cysts could be mapped, and the nature of the cysts could be identified according to the changes of the signal intensity between Tl and T2-weighted images. 3. The relationships of the cysts with the physis were well defined in MRI, and we could discern the presence of physeal injury in 15 cases. 4. Because anatomic details of cartilage, ligamentum teres, and joint fluid could be well differentiated with the MRI, arthrographic effect was obtained noninvasively. 5. Because the cartilage of the femoral head, that showed hypertrophy in MRI initially, was eventually ossified according to the serial follow-up roentgenograms, the final outcomes were predictable with the MRI in the relatively earlier stage. In summary, first, MRI could determine the presence of necrosis more sensitively and accurately, second, the locations and the contents of the metaphyseal cysts could be evaluated, third, MRI was useful in predicting the disturbance of the physis, fourth, arthrographic effect could be obtained, fifth, the final head shape was predictable.