Walking speed is a simple and reliable measure of motor function that is negatively associated with adverse health events in older people, including falls, disability, hospital admissions, and mortality. Lead has adverse affects on human health, particularly on the vascular and neurological systems. We explored the hypothesis that lead is associated with slower walking speed. We used U.S. National Health and Nutrition Examination Survey (NHANES) cross-sectional data from 1999-2002. The time to walk 20 ft (walking speed) was measured among 1,795 men and 1,798 women ≥ 50 years of age. The association between walking speed and quintiles of blood lead concentration was estimated separately in men and women using linear regression models adjusted for age, education, ethnicity, alcohol use, smoking status, height, and waist circumference. Mean blood lead concentrations and walking speeds were 2.17 μg/dL and 3.31 ft/sec in women, and 3.18 μg/dL and 3.47 ft/sec in men, respectively. Among women, walking speed decreased with increasing quintiles of blood lead, resulting in an estimated mean value that was 0.11 ft/sec slower (95% CI: -0.19, -0.04; p-trend = 0.005) for women with blood lead concentrations in the highest versus lowest quintile. In contrast, lead was not associated with walking speed in men. Blood lead concentration was associated with decreased walking speed in women, but not in men. Our results contribute to the growing evidence that lead exposure, even at low levels, is detrimental to public health.