There are many diagnostic tools for Legg-Cavle-Perthes Disease(LCPD) such as plain film, arthrography, Bone scan, CT scan and MRI. But no single method is universal to evaluate LCPD. Arthrography can show us true mechanical shape of femoral head and acetabulum and congruity of hip joint at various position in movement, so we can determine the method of treatment by arthrography. We performed arthrography on 36 hips in 34 children under treatment for LCPD. They were from three to twelve years old. 14 cases were avascular or fragmentation stage and 22 cases were reparative. 1 case was Catterall group II, 15 cases were group III, and 20 cases were group IV. We observed true contour of femoral head and joint congruity with acetabulum in arthrogram. We tried to determine the most congruous position of the hip. We calculated femoral head sphericity by caput index, lateral displacement by migration index and medial joint space and compared them with plane film. The results obtained were as follows. l. In normal hip the mean twice of epiphyseal index was 0.92, caput index in A-P projection was 0.95 and in frog-leg projection 0.99. 2. In disease hip the mean twice of epiphyseal index was 0.62, caput index in A-P projection was 0.82 and in frog-leg projection 0.90. 3. Sphericity of femoral head was more actual in arthrogram. Lateral displacement was not significantly different between plain and arthrogram. 4. Femoral head was more spherical during avascular than reparative stage and on frgo-leg than A-P projection. 5. Flattening of femoral head was mainly at superolateral aspect. 6. The main change of acetabulum was flattening at superolateral but variable. 7. Conguity and most congrous position of the hip joint could be seen in arthrogram. 8. Hinge abduction could be seen only in arthrogram.