To assess whether adiponectin gene (ADIPOQ) polymorphism is associated with intrauterine fetal growth and cord blood adiponectin, we investigated eight single-nucleotide polymorphisms (SNPs; rs182052, rs710445, rs16861205, rs12495941, rs1501299, rs3774261, rs2082940 and rs266729) in ADIPOQ and birth weight and cord blood adiponectin in 526 healthy neonates. We found that the neonates carrying the G allele of rs266729 had a significantly greater birth weight s.d. score than those homozygous for the C allele (CC: -0.06±0.75 versus CG: 0.20±0.64 versus GG: 0.07±0.78; P=1.65 × 10(-3), adjusted P=9.90 × 10(-3)). However, this difference was not significant after adjustment for cord blood adiponectin (P=0.04, adjusted P=0.26). The rs266729 SNP was strongly associated with cord blood adiponectin; neonates with rs266729 GG had the highest adiponectin (CC: 34.1±20.2 versus CG: 44.3±26.1 versus GG: 54.1±36.7 μg ml(-1), P=2.80 × 10(-9), adjusted P=1.68 × 10(-8)). This association remained after adjustment for birth weight s.d. score (P=6.63 × 10(-8), adjusted P=3.98 × 10(-7)). Our results suggest that the influence of the rs266729 SNP in ADIPOQ on birth weight may be dependent on circulating adiponectin.