Leptin is a cytokine-like hormone which is considered the link between fat and bone; it is produced by adipocytes and osteoblasts, regulates food intake via specific receptors located in the central nervous system (CNS) and bone mass through alternate pathways: one involving a direct stimulatory effect on bone formation; and another indirect effect through the CNS that suppresses bone formation. Leptin exerts a direct stimulatory effect on osteoblast differentiation and on bone growth if directly administered, while it exerts an inhibitory effect on bone formation if administered in the CNS. It is therefore unclear whether leptin should be considered an antiosteogenic factor or an anabolic agent for bone formation: in all probability, leptin has a broader role in human physiology and in particular its action has evolved in order to synchronize periods of bone growth, mineral accretion and fertility with periods of food availability, while it restricts growth and reproduction during periods of nutritional stress.