We used three-dimensional (3D) MRI to assess the sphericity of the cartilaginous femoral head in developmental dysplasia of the hip. We assessed 21 children using 3D-MRI. The smallest sphere including the femoral head cartilage was drawn, the diameter was measured, and the center of the sphere was defined. We compared the diameters of the femoral heads between unaffected and diseased sides. The diameter of the affected side was smaller, with flattening at the posteromedial area and proximoposterior areas. 3D-MRI showed that the shape of the dislocated femoral head was aspherical with focal growth failure.