Girls and young women with Turner syndrome ages 10 to 21 years will participate. The girls ages 15 to 21 years will randomly and double blindly receive treatment with either 2 mg or 4 mg estrogen for 5 years. Yearly examinations with blood tests, physical examinations, questionnaires, ultrasound and MR-scan of the internal female genitalia, DEXA-scan of the bones and MR-scan of the heart will be performed.