This study examines the reduction of the number of items in the scales of the Child Behavior Checklist, while maintaining the reliability and predictability of its original scales. For that purpose, the original scales were replicated with data from the Pittsburgh Youth Study. New, abbreviated scales were constructed using the most potent items. This process yielded trimmed scales that were highly correlated with the full scales and that still reflect the original meanings of the scales. Further, there was no loss of reliability or predictability with the trimmed as opposed to the full scales. The results were replicated in an analysis with identical variables from the Rochester Youth Development Study. This replication produced equally high reliabilities with similar levels of prediction of delinquent behavior.