High-dose estradiol therapy for reduction of final height may be complicated by severe side effects such as deep vein thrombosis. We report a 14.6-year-old girl with tall stature. In order to reduce final height she was treated with ethinylestradiol and medroxyprogesterone. After arthroscopy she suffered acute deep venous thrombosis of her left leg. Despite being monitored at short intervals, coagulation parameters such as AT III and protein C indicated no development of thrombosis. Medical height reduction with estrogen should be accompanied by heparinisation during longer-lasting periods of immobilisation.