A postmortem material of lumbar spines from individuals aged 0–25 years was studied. Spines from newborn mature or premature infants were generally straight or kyphotic above a well marked lumbo-sacral angle. The development of the lordosis takes place during the first 3 years after birth and commences before the children start to sit, stand or walk. Children who never assume the erect position develop a lumbar lordosis to the same degree and at the same time as other children. Growth retardation gives a delay in the emergence of the lumbar lordosis.