40 excessively tall girls with a mean height prediction of 182 cm were treated for serious psychosocial reasons continuously with ethinylestradiol 0.3 mg daily and with norethisterone 10 mg daily for 5-7 days every 4th week. Their age at the start of treatment ranged from 9.4 to 13.8 years, and the mean duration of treatment was 1.7 years. Bone age was assessed according to the TANNER-WHITEHOUSE-II (RUS) method, and height predictions were calculated using the age-specific regression equations of TANNER et al. Results were compared with those in 9 untreated control cases. Mean reduction of predicted height in all patients was 4.6 +/- 2.4 cm, and the most marked reduction was found in the youngest group of patients. However, even in patients after menarche and with a bone age above 14 years at start of treatment, there was still a considerable reduction of adult height. Bone maturation was accelerated by treatment (1.4 years per year), and the most marked acceleration was observed during the first 6 months (1.7 years per year). Growth velocity was normal or slightly subnormal during the first 6 months and very low thereafter. During treatment, there was a considerable weight gain which was, in part, lost again when treatment was discontinued. Posttherapeutic amenorrhea was infrequent, and normal and regular menstruations reappeared in the majority of the patients about 1 month after discontinuation. It is concluded that estrogen treatment in high doses is effective in reducing adult stature in girls and that somatic and psychological side effects are minimal when treatment is started after onset of spontaneous puberty. Although early treatment tends to give better results, beneficial results may still be obtained in older patients.