The aim of this study was to evaluate the effects of long-term exposure to polychlorinated biphenyls (PCBs) on developing dental enamel. 202 8- to 14-year-old children who were pre- and post-natally exposed to PCBs in the contaminated region of Bela Krajina, Slovenia, were studied. 202 controls from Brsljin were matched for age and sex. Risk assessment was based on the concentrations of toxic PCB congeners in the diet. Levels of PCBs in dentine were used to validate exposure. PCB levels were analysed by high-resolution gas chromatography. The prevalence of developmental defects of enamel was assessed using the FDI Index. Developmental defects of enamel in permanent teeth were found in 71.3% of exposed children, compared to 49.5% in the control group. The enamel was abnormal in 21.9% of the permanent index teeth of exposed children and in 12.7% of the control children. The difference was statistically significant (chi(2) = 84.18; p = 0.0019), mostly on account of demarcated opacities and hypoplasia. The extent of the defects was also greater in the exposed group (chi(2) = 61.3; p = 0.0001). No significant correlations were found between PCB exposure and developmental defects in deciduous teeth. In conclusion, our results showed that long-term exposure to PCBs may cause developmental defects of enamel.