The goals of this presentation are to review the essential roles of aromatase, estrogens and the estrogen receptor in pubertal growth. Estrogen deficiency due to mutations in the aromatase gene (CYP19) and estrogen resistance due to disruptive mutations in the estrogen receptor gene have no effect on normal male sexual maturation in puberty. However, they lead to absence of the pubertal growth spurt, delayed bone maturation, unfused epiphyses, continued growth into adulthood and very tall adult stature in both sexes. Gonadotropin and androgen levels are elevated in patients with either estrogen deficiency (aromatase deficiency) or estrogen resistance (estrogen receptor mutation). Glucose intolerance, hyperinsulinemia and lipid abnormalities are also present. Skeletal integrity is compromised. Increased bone turnover, reduced bone mineral density and osteoporosis develop in both sexes. Sexual orientation is appropriate in males and females. In females, aromatase deficiency in the ovary causes pubertal virilization and multicystic ovaries because of elevated gonadotropins and androgens. Simultaneously, secondary sexual maturation fails to occur. Placental aromatase deficiency results in virilization of the mother and her female fetus because of the accumulation of potent androgens which are not converted to estrogens. The male fetus has normal genitalia. In conclusion, estrogens are essential for normal female secondary sexual maturation, bone maturation, epiphyseal fusion, pubertal growth spurt and achievement of normal bone mineral mass. Estrogens also influence insulin sensitivity and lipid homeostasis. However, estrogens do not appear to be essential for fetal survival, placental growth, or female sexual differentiation.