Objective: To ascertain the association of childhood ADHD and oppositional defiant disorder (ODD) on functional impairment and to test the moderating influence of callous-unemotional (CU) traits. Method: Ethnically diverse 6- to 9-year-old children with (n = 59) and without (n = 47) ADHD were ascertained using multiple methods (i.e., rating scales and structured interview) and informants (i.e., parent, teacher, and interviewer). Results: Using ratings of impairment that were independent of the diagnostic assessment of ADHD and ODD, the association between ADHD and impairment was significantly moderated by CU traits, such that CU traits positively predicted impairment at low and moderate levels of ADHD but not at high levels of ADHD. CU traits did not moderate the association of ODD and impairment. Conclusion: The authors discuss findings within the context of multiple pathways to and from negative outcomes and the utility of evaluating CU traits in studies of ADHD and conduct problems. (Contains 4 tables and 3 figures.)