The availability of recombinant human growth hormone (GH) has resulted in investigation of the role of GH in adulthood and the effects of GH replacement in the GH-deficient adult. These studies have led to the recognition of a specific syndrome of GH-deficiency, characterized by symptoms, signs and investigative findings. Adults with long-standing growth hormone deficiency are often overweight, have altered body composition, with reduced lean body mass (LBM), increased fat mass (FM), reduced total body water and reduced bone mass. In addition, there is reduced physical and cardiac performance, altered substrate metabolism and an abnormal lipid profile predisposing to the development of cardiovascular disease. Adults with GH deficiency report reduced psychological well-being and quality of life. These changes may contribute to the morbidity and premature mortality observed in hypopituitary adults on conventional replacement therapy. GH treatment restores LBM, reduces FM, increases total body water and increases bone mass. Following GH therapy, increases are recorded in exercise capacity and protein synthesis, and "favourable" alterations occur in plasma lipids. In addition, psychological well-being and quality of life improve with replacement therapy. GH is well tolerated; adverse effects are largely related to fluid retention and respond to dose adjustment. It is likely that GH replacement will become standard therapy for the hypopituitary adult in the near future. The benefits of GH replacement in the GH-deficient adult have been unequivocally demonstrated in studies lasting up to 3 years. The results of longer term studies are awaited to determine whether these benefits are sustained over a lifetime.