Growth and maturation of the pelvis are complex but the process of endochondral ossification in the pelvis is the same as that in the long bones. Primary ossification of the pelvis is completed about 8 years of age, and secondary ossification is completed in the early twenties. Growth of the pelvis follows that of the rest of the body. The most rapid period of growth is in the first year of life. A stable rate of growth is attained after age 3 years until puberty. Basic sex differences in the adult pelvis are established in early childhood. Exterior dimensions of the pelvis are greater in boys, but interior dimensions of the pelvis are greater in girls. Much of the present knowledge about growth and maturation of the pelvis has come from radiographs. More current knowledge of pelvic growth is needed by those involved in automobile restraint design. Pelvic injuries are not uncommon to children in automobile accidents. A child's body is not similar to an adult's, so the results of pelvic injuries may produce life long problems.