The goal of this study was to examine the extent to which preschoolers with externalizing behavior problems (EBP) can identify behaviors indicative of callous-unemotional (CU) traits among their peers. Participants for this study included 86 preschool children (69% boys; M[subscript age] = 5.07 years) with at-risk or clinically elevated levels of EBP who were attending a summer treatment camp. Data collected from the children, their peers, and the counselors who worked at the summer camp examined preschoolers' social preference, likability, and behaviors indicative of CU. Parents and preschool teachers also reported on children's CU traits and severity of behavioral impairment, as well as school readiness. Peer nominations of CU traits showed (a) excellent factor structure as evidenced by clear CU items (e.g., "don't feel bad when they do something wrong") versus more prosocial items ("share," "cooperate"); (b) moderate construct validity when compared to counselor reports of the CU factor as well as preschool teacher reported ratings of CU traits and severity of behavioral impairment; and (c) good utility as evidenced by associations with peer and counselor rated social preference, likability, and school readiness measures as rated by both parents and preschool teachers. These findings indicate that as early as preschool, children with EBP can identify peers who engage in behaviors indicative of CU traits, which have significant implications for children's social status and overall school readiness. [This article was published in "Journal of Clinical Child and Adolescent Psychology," v45 n2 p201-214 2016.]