Children and adolescents with growth hormone (GH) deficiency (GHD) have reduced bone turnover and bone mass in comparison with normal individuals. GH replacement therapy stimulates bone turnover and improves bone mass during childhood and adolescence. At final height, patients with GHD treated with GH have normal mean values of bone mass, but some patients have reduced lumbar BMD (Z score <1) with an increased susceptibility to fractures. Children and adolescents with GHD have approximately a fourfold decreased fracture frequency during treatment in comparison with controls. The changes of bone mass during the transition to adulthood in patients with GHD who discontinued GH treatment after final height are not defined. An increase of lumbar BMD after final height has been reported until 2 years after discontinuation of GH treatment; this could be the result of a spontaneous progression towards peak bone mass or of a persisting effect of GH treatment on bone mass accumulation. GH has an important role in the accrual of bone mass during childhood and adolescence, but the impact of GHD on bone mass during the transiton to adulthood is unknown.