Abstract INTRODUCTION: It is well documented that low birth weight may increase the risk of chronic diseases, notably atherosclerotic cardiovascular disease, later in life. However, the mechanisms of maternal and fetal weight regulation during pregnancy are not clearly defined, and leptin might play a role in this process. This study was performed to compare the serum leptin levels in normal and intrauterine growth-retarded (IUGR) term neonates. In addition, we aimed to determine the relationships of maternal and neonatal leptin concentrations with birth weight. methods: From April 2005 to December 2005, serum leptin concentration was measured in umbilical cord and maternal venous blood samples of 32 mother-infant pairs with IUGR full-term neonates and 34 mother-infant pairs with normal full-term neonates. Independent sample t-test was used for the comparisons. The correlation analysis was performed by Pearson correlation coefficient. results: The mean leptin concentration in newborns with IUGR and in their mothers (2.82±1.95 and 3.16±2 µg/L, respectively) was lower than in infants with normal growth and their mothers (3.04±1.74 and 3.18±1.97 µg/L, respectively) but these differences were not significant. Cord blood leptin concentrations did not correlate with birth weights (r=0.02), BMI of neonates (r=0.033), or leptin concentrations of their mothers (r=0.17). When data of all newborn infants were collectively analyzed, cord blood leptin concentration in the IUGR group correlated with BMI of neonates (r=0.36, P=0.03) but not with birth weight (r=0.22, P=0.20). There was no significant difference in terms of gender. CONCLUSIONS: Cord blood leptin levels appear to correlate with BMI, as an indicator of fat mass, but not the birth weight of IUGR neonates. In addition, maternal leptin concentration cannot be considered as an accurate indicator of fetal growth. Keywords: Leptin, intrauterine growth retardation, cord blood, neonate.