Turner syndrome is also known as congenital ovarian hypoplasia. There are 23 pairs of 46 human chromosomes, one of which is the sex chromosome, the X and Y chromosomes in boys and both sex chromosomes in girls. If a girl has only one X chromosome, or if part of the X chromosome is missing, she may develop Turner syndrome, a congenital ovarian hypoplasia. A Turner syndrome fetus may have millions of germ cells in the middle of the mother’s pregnancy, but this rapidly decreases, leaving only a few follicles in the fibrous cords at birth, resulting in hypogonadism and decreased estrogen production. The effects of hypogonadism are not limited to the reproductive system, but can affect many systems, organs or tissues as follows: Skeletal system: Bone growth and mineral gains are dependent on the presence of estrogen. Low doses of systemic estrogen combined with growth hormone can increase the final adult height of children with Turner syndrome, and estrogen deficiency leads to osteoporosis in Turner syndrome. Cardiovascular system: Low estrogen levels can affect vascular endothelial function in Turner syndrome patients, and this is supported by the fact that oophorectomy is an independent predictor of myocardial infarction and sudden coronary death. A major risk factor for cardiovascular events in patients with Turner syndrome is hypertension, which affects 25% of adolescents and 40C60% of adults with Turner syndrome. Therefore, blood pressure should be measured at every visit and ambulatory blood pressure monitoring should be performed for a more accurate diagnosis of hypertension and assessment of outcome. Lipid metabolism: Low estrogen levels may cause abnormal lipid metabolism, increased centripetal fat and early atherosclerosis in patients with Turner syndrome. Glucose metabolism: Low estrogen levels may lead to decreased insulin production, insulin resistance and a significantly higher incidence of diabetes mellitus in patients with Turner syndrome. Liver function: Patients with Turner syndrome may have abnormal liver enzymes, which can be improved by estrogen replacement therapy. Neurological: Low estrogen levels in patients with Turner syndrome can cause some cognitive deficits (short-term memory, reaction time and non-verbal processing speed), which can also be improved with estrogen replacement therapy.