Objective This study aims to establish a cut score for the Inventory of Callous‐Unemotional Traits, a well‐validated measure of callous‐unemotional (CU) traits in youth for which there is currently no cutoff score. Method We analyzed data on 634 adolescents from high schools (n = 343) and juvenile detention centers (n = 291). Participants, their parents and guardians, and their teachers and staff members reported on participants’ CU traits and aggressive/violent behavior. Results All three reports of CU traits as well as intersource composites were associated with aggression, violence, and detained status. Parent report was a better indicator compared to self‐reports and teacher reports. Appropriate cut scores based on each report and composite were determined. Conclusion We recommend that information from all available informants should be used whenever possible, but when only one informant report is feasible, parent reports are preferable.