Lead is often present in our environment, but its effect on thyroid function is still unclear. In this study, multiple linear regressions were performed between log-transformed blood lead levels and thyroid function parameters of 4652 adults from the 2007-2008 National Health and Nutrition Examination Survey. The models were adjusted for age, gender, race/ethnicity, smoking, alcohol consumption, body mass index, physical activity, iodine intake, medications, and bone mineral density. Blood lead concentrations (mean: 1.52 ± 1.20 μg/dL [range 0.18-33.12]) were inversely associated with total thyroxine (regression coefficients [β]: -0.22 [95% CI: -0.34, -0.09] in the general population, but were not correlated with thyroid stimulating hormone, total or free triiodothyronine, nor free thyroxine. Blood lead may have no effect on the thyroid function; however, it could be associated with decreased concentrations in thyroid-binding proteins.