Aromatase enzyme is a cytochrome P450 protein that can catalyze the aromatization of C 19 androgens and thus their conversion into estrogens. It is tissue-specifically expressed in primate placenta, connective tissue, ovary, and brain through alternative splicing of tissue selective promoters. Human aromatase activity is critical for maintenance of early and mid pregnancy and in regulating parturition in late pregnancy. It is also important in the development of fetal gonadocytes and the sexual differentiation of brain, especially the hypothalamic-gonadal axis. Exposure to aromatase inhibitors in primates significantly impairs pregnancy outcome. Recent case reports have described syndromes associated with rare autosomal recessive mutations in aromatase genes.