Developmental dysplasia of the hip (DDH) includes various abnormalities such as instability, subluxation, and dislocation. In selecting the appropriate treatment method, it is important to distinguish these abnormalities from each other. We developed a novel approach for diagnosing DDH using three-dimensional MRI, which are used to visualize the spatial relation between the dislocated femoral head and the acetabulum and to clarify the changes during hip joint movement. The three-dimensional MRI are useful for confirming the diagnosis of DDH and for evaluating the reducibility of the affected hip.