Bone marrow transplantation (BMT) has increased significantly in the last decade and encompasses allogeneic and autologous transplantation of stem cells from bone marrow, peripheral blood and umbilical cord blood. Bone marrow transplantation is mainly used to treat patients with poor prognosis leukaemia but also other advanced or relapsed cancers and non-malignant disorders, so that now between 30 000 and 40 000 transplants are performed world-wide per year (Horowitz, 1998).The success story in transplantation medicine, however, has resulted in significant endocrine late effects both in children and adults including thyroid, pituitary and gonadal dysfunction, with adverse effects on the growth of children. The relative risk of these adverse events is influenced by the underlying pathological condition, previous treatment for that condition, the use of total body irradiation (TBI) and the irradiation schedule, and the nature and quantity of the cytotoxic drugs used in the BMT preparative regimen.