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BACKGROUND: Attention deficit/hyperactivity disorder (ADHD) and lead exposure are high-prevalence conditions among children. OBJECTIVE: Our goal was to investigate the association between ADHD and blood lead levels (BLLs) in Chinese children, adjusting for known ADHD risk factors and potential confounding variables. METHODS: We conducted a pair-matching case--control study with 630 ADHD cases and 630 non- ADHD controls 4--12 years of age, matched on the same age, sex, and socioeconomic status. The case and control children were systematically evaluated via structured diagnostic interviews, including caregiver interviews, based on the Diagnostic and Statistical Manual of Mental Disorders, 4th ed., revised criteria (DSM-IV-R). We evaluated the association between BLLs and ADHD using the Pearson chi-square test for categorical variables and the Student t-test for continuous data. We then performed conditional multiple variables logistic regression analyses with backward stepwise selection to predict risk factors for ADHD. RESULTS: There was a significant difference in BLLs between ADHD cases and controls. ADHD cases were more likely to have been exposed to lead during childhood than the non-ADHD control subjects, with adjustment for other known risk factors [children with BLLs = 10 µg/dL vs. ≤ 5 µg/dL; OR = 6.0; 95% confidence interval (CI) = 4.10--8.77, p < 0.01; 5-10 µg/dL vs. ≤ 5 µg/dL, OR = 4.9; 95% CI = 3.47--6.98, p < 0.01]. These results were not modified by age and sex variables. CONCLUSIONS: This was the largest sample size case--control study to date to study the association between BLLs and ADHD in Chinese children. ADHD may be an additional deleterious outcome of lead exposure during childhood, even when BLLs are < 10 µg/dL. [ABSTRACT FROM AUTHOR]