Hip arthrograghy is a valuable procedure for visualization of the intrinsic obstructive factors impeding closed reduction and for critical assessment of quality of reduction in developmental dislocation of the hip. The authors have analyzed 25 cases of developmentally dislocated hips in 24 patients who have been followed up for more than 1 year postoperatively by roentgenographies and arthrographies. Among them 16 cases in 16 patients who had been treated by closed reduction according to acceptable quality of initial reduction were studied to estimate a value of arthrography and to evaluate an outcome of closed rediction performed on the base of an arthrographic finding. The following results were obtained. 1. The frequency of the common arthrographic observations were assessed. Medial dye columns identifying the depth of reduction were observed 25 cases(100%), configuration of osteocartilaginous structures in 24 cases(96.0%), limbus in 24 cases(96.0%), and ligamentum teres in 18cases(75.0%). 2. Good closed reduction classified according to Race and Herring on initial arthrography was associated with rapid improvement of acetabular angle and the CE angle and low incidence of avascular necrosis, compared with adequate or poor reduction. 3. In cases of initial good and adequate reductions, initial AP arthrograms showed some dye filling shadows owing to folding or redundancy of lax joint capsule of the dislocated hip after reduction just lateral to the limbus, of which finding decreased markedly on the second arthrograms. 4. The widths of medial dye column decreased with time during the first postoperative 7 weeks by an average of 0.5mm in cases with initial good quality of reduction, 3.5mm in adequate reductions and 0.5mm in poor reductions. 5. In cases with adequate closed reduction on initial arthrogram, but without substantial decrease in width of medial dye column on the second arthogram the outcome was poor. In those cases with decrease in width of medial dye column on the second arthrogram compared with initial arthogram, the shorter the period of immobilization in a plaster cast was, the worse eventual result was. 6. We think that hip arthography is a helpful procedure for visualization of obstacle obstructing closed reduction and for determination of treatment modality in developmental dislocation of the hip.