['Programming of the nutritional and hormonal status of offspring occurs mostly during the gestational and breastfeeding periods. Several studies have reported that breastfed children are more protected from developing obesity in adult life; however, the mechanism that explains this phenomenon is not clear. We undertook this study to evaluate if weight, gender or feeding mode (breastfed or formula-fed) affects leptin levels (during the first 3 months after birth) in a cohort of term newborns, the Breastfeeding Cohort.', 'A cohort of 99 term newborns divided into four groups according to gender and feeding type: breastfed female, formula-fed female, breastfed male and formula-fed male were studied. Feeding mode was freely chosen by the parents. Blood sampling for glucose, insulin and leptin was performed at birth and after 3 months.', 'No differences were found among the groups for maternal age, marital status, educational and socioeconomic level, maternal occupation, and prenatal care. No statistically significant differences were found for weight, length or body mass index at birth among the four groups. There were differences in leptin with a higher level in girls (0.907 ± 0.332) than boys (0.663 ± 0.351; p <0.001) at birth and at 3 months (0.618 ± 0.225, 0.464 ± 0.195; p <0.0001). A decrease in leptin levels from birth to 3 months was observed in all groups with the exception of breastfed females (0.849 ± 0.352-0.672 ± 0.222, p = NS).'] Is typical leptin fall mitigated by breastfeeding in female infants?