Estrogen influences brain development in females at puberty. Environmental and cultural factors interact with the biological effects of estrogen on the brain and consequently on cognition and behavior. Turner syndrome females lack endogenous estrogen as a result of dysgenetic ovaries. Turner syndrome therefore represents a unique, estrogen-deficient model in which to study the biological effects of estrogen on cognition and behavior. The specific aims of this project are to: 1) document further, the cognitive differences between girls with Turner syndrome at ages 5 to adult (less than or equal to age 50) versus age-matched, female controls. 2) to examine the differential effects of continuous estrogen replacement in infancy and in early childhood on cognitive and social function in a unique, previously approved, randomized, double-blind, placebo-controlled, treatment trial (87-CH-0152). Specifically, we hypothesize that estrogen replacement in early childhood will reduce the cognitive deficits of girls with Turner syndrome. In addition, we hypothesize that the degree of socialization ability in these girls will correlate with social-behavioral and social recognition ability. Finally, we hypothesize that earlier (infancy to 8 years) and longer estrogen replacement will result in less impairment of visual-motor ability, visual-spatial ability, socialization ability, and affective competence compared to later (9 to 12 years) estrogen replacement in girls with Turner syndrome.