Six major adverse medical events (AMEs) and 44 minor AMEs were recorded in 6 and 23 patients, respectively, during human growth hormone (GH) treatment of Turner syndrome, equivalent to 118 treatment years. During the first year of GH treatment, there was no change in the SD score (SDS) for systolic or diastolic blood pressure. In a subgroup of 20 patients, there was no change in psychological tests, oral glucose tolerance, glycosylated haemoglobin or serum triglycerides over the first year of GH treatment. The mean total serum cholesterol level fell over this period. The low incidence of adverse medical problems during GH treatment complemented its efficacy. Height velocity in the first year was 7.7 ± 1.8 cm/year (mean ± SD) and was correlated with maternal height SDS, though not with paternal height SDS. Some 36% of first-year height velocity SDS could be predicted by the dose of GH and maternal height SDS.