The reproductive activity is closely related to the nutritional status of the organism. A new hormone – leptin has been discovered a few years ago, which informs the brain about fat supplies in the body. Leptin participates in the regulation of the reproductive system at both, peripheral and central, levels. There are discussions about leptin as a possible trigger of puberty. The prepubertal leptin levels are low in both sexes, they increase with the onset of puberty. It has been suggested that leptin resistance might exist in the childhood, allowing the onset of the puberty only at the moment, when the adipose stores are adequate for the strongly demanding period of the adolescence. The role of leptin in pathogenesis of polycystic ovary syndrome (PCOS) is studied. The significance of leptin during pregnancy and after birth remains still unclear.

        Key words: BMI, leptin adipocytes, obesity, puberty, polycystic ovary syndrome, pregnancy