Results from the first randomized, controlled trial of growth hormone (GH) therapy in girls with Turner syndrome (TS) followed to final height firmly establish that GH increases final adult stature. It is widely believed that the efficacy of GH is dependent upon the duration of therapy and dosing (longer duration and higher dose give taller final height). In a recent observational study involving more than 1500 French girls with TS, multivariate analyses demonstrated that the age at initiation of GH therapy accounted for a large percentage of the variance (44%) in response. Age at initiation of estrogen therapy was the second most important factor in determining GH effect (later initiation, taller final height), accounting for 22% of the variance. Overall, 0.3 cm in adult height was gained for every year that estrogen therapy was delayed. However, analyses of the French data restricted to patients with induced puberty revealed that those treated with percutaneous estradiol attained a height 2.1cm taller than those using oral estradiol or other estrogen preparations. In another study, girls receiving GH therapy (n=14) who were randomized to receive intramuscular (IM) depot estradiol early (12.0-12.9 years) attained at least as much height as those who initiated it late (14.0-14.9 years). These results are consistent with the observations in adult women that oral estrogens decrease IGF-I serum levels and suppress the IGF-independent metabolic effects of GH, while transdermal estrogens do not. Taken together, these studies suggest that girls with TS should begin GH therapy as soon as growth failure is demonstrated and that puberty should be induced with transdermal or IM estradiol. Girls for whom height is normalized with GH therapy in early childhood have the opportunity to undergo puberty at an age-appropriate time and still achieve a normal adult stature.