Aim: To study the effects of growth hormone (GH) deficiency (GHD) and GH replacement therapy (GHRx) on bone mineral density (BMD) and body composition. Methods: 59 GHD children participated (age range 0.4-16.9 years); the follow-up period was 6 years. Lumbar spine BMD (BMDLS), total-body BMD (BMDTB), and body composition were measured prospectively using dual-energy X-ray absorptiometry. Results: Mean BMDLS and BMDTB were significantly reduced at the time of the diagnosis. The bone mineral apparent density of the lumbar spine (BMADLS) was reduced to a lesser degree. The BMADLS increased to normal values after 1 year; BMDLS and BMDTB normalized 1 year later. At the time of the diagnosis, the lean body mass was reduced and steadily increased during GHRx. Percentage of body fat was increased at baseline and normalized within 6 months. The severity of GHD was not associated with the BMD at diagnosis or the response to GHRx. Conclusion: Areal BMDLS and BMDTB and, to a lesser extent, BMADLS are decreased in GHD children, but normalize within 1-2 years.