Aim: To evaluate haemostatic effects and clinical outcome of oestrogen treatment of constitutionally tall stature in girls. Methods: We conducted a single-centre cohort study, 63 girls referred over a period of 15 years were investigated. The girls were given oestrogen treatment for constitutional tall stature at a median initial dose of 300 ug ethinyl estradiol/day and were consecutively examined for changes in coagulation. Medical records were retrospectively reviewed, additional data were collected at follow-up by blood sampling and interviews. Results: After 1 year of treatment, levels of antithrombin and von Willebrand factor (VWF) were significantly decreased (p < 0.001 and p = 0.015, respectively), whereas there was no significant change in levels of plasminogen inhibitor type 1. No venous thromboembolism (VTE) or major side effects were observed. Genetic risk factors for thrombosis were present, as was expected. The mean height reduction was 5.5 cm. The height-reducing effect was inversely correlated with chronological age (r =-0.44, p < 0.01) and bone age (r =-0.61, p < 0.01). Conclusions: Changes in coagulation parameters occurred both towards pro- and anticoagulation. Treatment with high-dose ethinyl estradiol can successfully limit final height, and it is most effective when started at a younger bone age.