Bone and mineral metabolism is regulated by numerous hormones and local growth factors. Growth hormone (GH), directly and/or indirectly through local IGF1 and IGF2 production, stimulates bone turnover as it increases osteoblast number and function. It also stimulates bone resorption through unknown mechanisms. GH (by IGF1) stimulates the renal 25-hydroxyvitamin D-1 alpha-hydroxylase activity and therefore enhances calcium and phosphate absorption in the intestine. It also increases the maximal renal tubular reabsorption of phosphate. The overall effect of GH on bone therefore seems beneficial as bone mass is increased together with the lean body mass. Large excess of GH, however, also increases the risk of osteoarthritis and has other serious metabolic side effects, so that its place in the treatment/prevention of osteoporosis is yet to be defined.