This meta-analysis examined the association between conduct problems and lead exposure. Nineteen studies on 8,561 children and adolescents were included. The average "r" across all 19 studies was 0.19 (p less than 0.001), which is considered a medium effect size. Studies that assessed lead exposure using hair element analysis yielded considerably larger effect sizes than those that assessed lead exposure using blood, tooth, or bone lead levels. Excluding the 3 hair analysis studies, the average "r" was 0.15 (p less than 0.001). The age of the participants did not significantly moderate the relation between lead exposure and conduct problems. Overall, the relation between lead exposure and conduct problems was strikingly similar in magnitude to the relation between lead exposure and decreased IQ. (Contains 1 table and 1 footnote.)