Demonstration of the long-term efficacy of GH replacement in GH-deficient adults has depended on a combination of single-centre studies and data from large multinational databases, which, by virtue of their size, are likely to detect rare adverse events and also permit analysis of mortality rates. The Pharmacia International Metabolic Surveillance (KIMS) study (a pharmacoepidemiological survey of the safety and efficacy of GH replacement in adults, sponsored by Pharmacia) is currently the largest database, with information on over 8000 patients from a total of 27 countries. Abundant epidemiological evidence confirms that hypopituitarism is associated with premature mortality, with an increase in cardiovascular and cerebrovascular disease as a primary underlying cause. Central adiposity, hyperlipidaemia, insulin resistance, and diabetes mellitus are common in adults with hypopituitarism. GH replacement is associated with improvements in central fat mass and mean reductions in serum total and low-density lipoprotein cholesterol which may be additive to those achieved with hydroxymethylglutaryl-coenzyme A reductase inhibitors. These beneficial effects are maintained for at least 2 Years after initiation of therapy, as are reductions in central adiposity, with similar benefits seen in men and women when the GH dose is titrated to achieve a serum IGF-I between the median and the upper end of the age-related reference range. Fasting plasma glucose and glycated haemoglobin increase, usually within the reference range, during prolonged GH replacement, but do not tend to rise further above baseline in subjects with pre-existing impaired glucose tolerance. Bone remodelling increases during GH replacement therapy, but indices tend to return to baseline within 5 Years of commencing treatment. Bone mineral density increases in men whereas, in women, improvement is limited to stabilisation of bone density. Data from the KIMS study demonstrate that prolonged GH replacement is associated with a reduction in the number of patients requiring assistance with daily living and a significant reduction in sick leave and hospital admissions. GH replacement therapy improves psychological well-being, particularly in those patients with the greatest deficit prior to treatment, with improvement maintained beyond 6 Months of therapy and sustained during long-term follow-up. Data from the KIMS population show that there is no increase in the overall occurrence of de novo neoplasia or the rate of regrowth of primary pituitary tumours. There is an apparent increase in intracranial neoplasia, which may be an artefact of comparing a surveillance population with general population data. Unlike mortality in untreated hypopituitary GH-deficient patients, mortality in the KIMS study is currently similar to that predicted for the normal population.