Three groups of girls with mean final height predictions of 185.3 cm were treated in 3-week cycles with 0.25, 0.5, or 1.0 mg of ethinylestradiol. The three groups were comparable with regard to chronological age, bone age, height prediction, and duration of treatment. Reduction in final height of 5.5-5.9 cm/group in comparison with the initial prediction was observed in all treated groups. This reduction appeared independent of estrogen dose. Subsequent height increases were limited to about 50% of the predicted gain in all cases. In a comparable group of untreated tall girls the prediction method overestimated the final height by 1.2 cm. In the groups receiving 1.0 and 0.5 mg EtE2 a significant reduction in IGF-I levels was achieved within three to six months after the start of estrogen therapy.