The ovarian hormones stimulate the development of the reproductive system, induce the development of secondary sexual characteristics, and promote a receptive endometrium for the growth and development of the proconceptus. The development of the ovary is dependent on local and endocrine factors that can be the target of endocrine disruptors. The T-shaped uterus seen in women exposed to diethylstilbestrol (DES) could represent a narrow and more branched structure, similar to the structure of the fallopian tube. Müllerian development is dependent on coordinated gene expression and hormone exposure. The genes that control normal patterning of the reproductive tract are beginning to be identified. The most important hormones regulating mammary gland development are estrogen and progesterone. During pregnancy and lactation, prolactin contributes to lobular differentiation and milk production. Estrogen and progesterone play a fundamental role during puberty to develop a normal adult breast.