Bone mineral density (BMD) increases during growth until a peak is reached at maturity. The risk of development of postmenopausal osteoporosis depends on the peak bone density and the rate of its subsequent loss. To identify whether low weight at birth could affect the peak bone density, we measured BMD at both the lumbar spine and femoral neck using dual energy X-ray absorptiometry (DXA) in a group of women who had low weight at birth and in a control group of normal birth weight. There was no significant correlation between the weight at birth and the adult BMD. It appears, therefore, that low weight at birth does not influence the peak bone density and that prematurity is not a risk factor for osteoporosis.