||This study compared difficulties in emotion regulation among primary, secondary, and low callous-unemotional (CU) youth in a sample of 417 detained adolescents (306 boys, 111 girls). Mixture modeling on the basis of posttraumatic stress disorder (PTSD) symptoms identified two groups of youth high in CU traits consistent with primary and secondary CU. Youth were typologized on the basis of PTSD symptoms which represents a novel method that is consistent with the theory underlying secondary callousness. Compared to youth classified in the primary group, youth classified as secondary CU reported higher levels of PTSD symptoms, anxiety, trauma exposure, and difficulties with clarity of emotions and nonacceptance of emotions. Difficulties in emotion regulation reported by youth in the secondary versus primary groups may be related to processes involving emotional numbing in the aftermath of posttraumatic distress. The results of the current study have implications for the classification of primary and secondary CU as well as the clinical treatment of youth with these characteristics.