The effects of different doses of oestrogens in constitutionally tall girls were evaluated in two centres for paediatric endocrinology. In one centre, 38 girls were treated with a high oestrogen dose of 0.3 to 0.5 mg ethinyloestradiol (EE) daily. In the other, 44 girls received a comparably low dose of 0.1 mg EE per day. Height prediction (HP), chronological age (CA), and height at the onset of treatment were comparable in both groups. Although the duration of treatment was significantly longer in those receiving the low dose, the cumulative oestrogen dose was still significantly lower. The dose of EE had no effect on final height reduction (high dose group: 4.9±2.6 cm, low dose group: 5.1±2.4 cm). Final height was more reduced in both groups when treatment was started at an early bone age (BA) (≤13 years). No serious side effects were observed in either group, however weight gain was more pronounced in girls receiving the higher dose. We conclude that treatment of constitutionally tall girls with low doses of oestrogens is equally effective in reducing the final height as the usually administered high doses. The lowest effective dose has to be determined in a randomized, prospective clinical trial.