The hypothalamus plays an essential role in controlling appetite during adult life. It undergoes tremendous growth beginning early in gestation and continuing during the postnatal period. During this developmental period, a variety of processes shape the hypothalamic nuclei involved in the control of eating. These include the birth of new cells that populate these areas (neurogenesis), the migration of these cells to their final destinations, selective neuronal death, and, finally, the development of functional neural connections. Each of these developmental processes represents an important period of vulnerability during which alterations of the pre- (intrauterine) and early postnatal environments may have long-term and potentially irreversible consequences on hypothalamic development and function. Metabolic hormones, including the adipocyte-derived hormone leptin, have recently emerged as likely mediators of the environmental nutrient-sensing apparatus that directs hypothalamic programming.