The Child Behavior Checklist (CBCL) and related material, developed by Achenbach and Edelbrock in Vermont, was validated in a mailed survey. A population based sample of 779 children between the age of four and 17 years was compared to a sample of 146 children referred for child psychiatric service. Danish children scored very much like our Scandinavian and German neighbours, but low compared to most others. The CBCL mean 'total behavior problem score' in the population was 17.7. The checklists, especially the parent and teacher versions, provided good construct validity. Youths generally reported more emotional problem behavior than their parents and teachers did about them. In general, parents and youths agree more, reporting emotional problems, and parents and teachers agree more, when scattering externalizing behavior. Short screening constructs are introduced, and by the use of latent trait analysis, four clinically relevant sub-scales were generated. Predictive value, sensitivity, specificity and clinical validity must be undertaken in a future two-phase study.