Growth hormone and related growth factors are essential for normal childhood development, secretion rate then declining from early adulthood. Adults with growth hormone deficiency, e.g. after pituitary ablation, have many clinical features such as reduced muscle and bone mass which are also seen in healthy older people. In both cases, growth hormone treatment at least partly reverses these changes. This has led to the rather elegant notion that growth hormone decline may be responsible for age-related involution and death and raises the prospect of hormonal replacement therapy for aging and frailty.