The authors examined the association between maternal polychlorinated biphenyl (PCB) levels and risk of neural tube defects (NTDs) in Mexican American women with NTD-affected pregnancies who resided in the 14 Texas-Mexico border counties during 1995-2000 (cases). Controls were randomly selected from study area women delivering normal live births. For PCB congeners with sufficient numbers of detectable values (PCB 99, 101, 110, 118, 138, 153, 180), there was little association between the proportions with detectable PCB levels in cases and controls. Odds ratios were <1 or compatible with the null, but power was low for some congeners. An index of seven PCB congeners (105, 118, 138, 153, 170, 180, 194) was also not associated with NTD risk. The maternal serum PCB levels in this study population (median PCB 153 level: 18 ng/g) were comparable to those with background exposure and do not appear to have contributed to the high prevalence of NTDs in this population.