Objective-To study the association between "pregnancy" prevalence (aVected births and terminations) of neural tube defects in postcode districts of Glasgow and lead concentrations in domestic water. Setting-Postcode districts of Glasgow supplied by water from the Loch Katrine reservoir. Design-An ecological study. Lead concentrations from 1911 randomly selected domestic water samples were obtained from the Glasgow 93 lead study. Neural tube defects (aVected births and terminations) were identified from the Glasgow register of congenital anomalies for the period 1983-95 for each postcode district in the study population. Correlations were sought between lead concentrations and pregnancy prevalence of neural tube defects/1000 live births in postcode districts. Results-No correlation was found between domestic water lead concentrations > 10 µg/litre and pregnancy prevalence of neural tube defects within postcode districts. Areas of Glasgow previously with high domestic water lead concentrations did not have a higher prevalence of neural tube defects. Houses with the lowest domestic water lead concentrations were in Carstairs deprivation categories 1 (least deprived), 6, and 7 (most deprived). The highest pregnancy prevalence of neural tube defects was found in the most deprived areas. Conclusion-Deprivation is a risk factor for neural tube defects and might have been a confounding factor in previous studies looking at the association between such defects and domestic water lead concentrations. This study does not support the hypothesis that levels of lead > 10 µg/ litre in domestic water supplies are associated with a higher pregnancy prevalence of neural tube defects. The reasons behind the decline in pregnancy prevalence of neural tube defects seen in the past two decades remain unexplained. (Arch Dis Child 2000;82:50-53)