The aim in this study was to determine the factors affecting leptin and soluble leptin receptor (sOB-R) levels in term small for gestational age (SGA) and appropriate for gestational age (AGA) newborns. The study group consisted of SGA (n=20) and AGA (n=20) newborns and their mothers. The leptin and sOB-R levels were tested using the ELISA method. The cord blood leptin concentrations were found significantly higher in the AGA group than in the SGA group (p=0.048). It was observed that cord blood leptin levels increased as body weight increased in the AGA group (r=0.681, p=0.001). The cord blood leptin levels were found higher in female infants than male infants (p=0.021). The plasma leptin levels were higher in the mothers of SGA neonates than those of AGA neonates (p=0.014). A positive correlation was detected between cord blood and amniotic fluid sOB-R concentrations in the AGA group (AGA: r=0.492, p=0.028). We conclude that the main determinants of leptin in SGA and AGA newborns are different. We can state that birth weight and gender are the main determinants of leptin levels in healthy neonates, but factors other than birth weight and gender may contribute to leptin levels in SGA newborns.