Studies have investigated associations between the Child Behavior Checklist (CBCL) and clinical diagnoses without assessing the impact of comorbidity on these results. This study evaluates associations between parental reports from the CBCL and a structured diagnostic interview in children with attention deficit disorder with hyperactivity (ADDH) stratified by the presence (ADDH+) or absence (ADDH-) of psychiatric comorbidity. Interview-defined ADDH children scored significantly worse on all scales of the CBCL compared with scores from interview-defined non-ill comparisons. However, these findings were accounted for by the subgroup of children with ADDH+. The results indicate a good correspondence between CBCL-based ratings and interview-defined diagnoses. These findings also suggest that the CBCL may be a good screening instrument, not only for ADDH but also for comorbid psychiatric disorders.