The adverse health effects of lead exposure in children are well described and include intellectual and behavioral deficits, making lead exposure an important public health problem. No safe blood lead level (BLL) in children has been identified. To estimate the number of children aged 1-5 years in the United States at risk for adverse health effects from lead exposure and to assess the impact of prevention efforts, CDC analyzed data from the National Health and Nutrition Examination Survey (NHANES) from the periods 1999-2002 to 2007-2010. This report summarizes the results of that analysis, which indicated that the percentage of children aged 1-5 years with BLLs at or above the upper reference interval value of 5 µg/dL calculated using the 2007-2010 NHANES cycle was 2.6%. Thus, an estimated 535,000 U.S. children aged 1-5 years had BLLs ≥5 µg/dL based on the U.S. Census Bureau 2010 count of the number of children in this age group. Despite progress in reducing BLLs among children in this age group overall, differences between the mean BLLs of different racial/ethnic and income groups persist, and work remains to be done to reach the Healthy People 2020 objective of reducing mean BLLs for all children in the United States (EH-8.2).