Polybromodiphenyl ethers (PBDEs) were analyzed in blood serum of pregnant women and in cord blood serum of their newborns from a general population cohort (n=174; Valencia, Spain). The most abundant PBDE congeners identified were BDE 47, BDE 99, BDE 153, BDE 154 and BDE 209. Their cord blood serum concentrations were about 45% of those in maternal serum but after lipid normalization about the same concentrations were observed in both types of samples. Thus, median of total PBDEs was 9.6ng/g lipid in cord serum (range between not detected and 140ng/g lipid) and 9.6ng/g lipid in maternal serum (range between not detected and 120ng/g lipid). The distributions of these compounds were dominated by BDE 47 in both cases. In cord blood serum the decreasing order of abundance was BDE 47>BDE 99>BDE 209>BDE 153>BDE 154. The congener composition in maternal serum followed a similar trend: BDE 47>BDE 153>BDE 154>BDE 209>BDE 99. The congener concentrations exhibited a higher degree of correlation in cord blood than in maternal serum. Use of the maternal determinants for categorization of the observed maternal and fetal PBDE concentrations only showed significant associations for the levels in umbilical cord. Neonates from rural areas exhibited statistically significantly lower concentrations than those from urban, semi-urban or metropolitan sites. Maternal serum also showed this difference but the higher dispersion of the concentrations in maternal serum did not afford its recognition with statistical significance. The lower qualitative and quantitative variability in the PBDE concentrations of cord blood serum than maternal serum suggest that the latter is reflecting PBDE contributions from a wider diversity of sources than the former whereas cord blood sera seem to represent the long term standing stock of these compounds accumulated in the maternal tissues.