In Turner's syndrome there is marked heterogeneity of growth response to growth hormone (GH) therapy. The study aim was to identify pretreatment factors that influence response to GH therapy. The 70 subjects recruited were prepubertal, had not received sex steroids and had received 28 units/m2/week of GH for > or = 1 year. Pretreatment variables associated with the greatest improvement in height SDS (r2 = 0.58) were weight for length index (p = 0.0001), target height (p = 0.004), bone age delay (p = 0.008) and age (p = 0.04). In conclusion, during two years of GH therapy the best growth response occurred in girls who were younger, heavier, had a delayed bone age and tall parents. Height SDS as a continuous variable is the most effective measure of growth when considering pretreatment factors that may influence response to GH therapy.