The purpose of this study was to examine the maternal and cord long-chain polyunsaturated fatty acid (LCPUFA) concentrations and their associations with birth outcome in term deliveries. Pregnant women (n = 253) delivering at term were divided into two groups based on their babies' birth weights (1) normal birth weight (NBW), that is, ≥2.5 kg (n = 190) and (2) low-birth weight (LBW), that is, <2.5 kg (n = 63). Each group is further divided into two groups according to the baby's sex, that is, male NBW (M-NBW), female NBW (F-NBW), male LBW (M-LBW), and female LBW (F-LBW) groups. Maternal plasma docosahexaenoic acid and erythrocyte arachidonic acid (AA) levels were lower (P < 0.05 for both), while cord plasma docosahexaenoic acid and erythrocyte AA levels were higher (P < 0.05 for both) in LBW group when compared to the NBW group. Maternal erythrocyte AA levels were positively associated with birth weight (P = 0.001), while cord plasma docosahexaenoic acid levels were negatively (P = 0.05) associated with birth weight. Reduced maternal and increased cord LCPUFA levels exist in mothers delivering LBW babies, especially in mothers delivering female babies, indicative of sex-specific effects. Am. J. Hum. Biol., 2011. © 2010 Wiley-Liss, Inc.