The Inventory of Callous Unemotional Traits (ICU) is the most commonly used measure of Callous Unemotional (CU) traits. However, its internal consistency reliability estimates vary substantially across different studies. This article reports findings from a reliability generalization (RG) meta-analysis, which included 146 studies (N = 64,356), to estimate the overall Cronbach's alpha values of ICU scores. Mixed-effects moderator analyses were also conducted to investigate possible study characteristics that may influence alpha values. The findings showed that the mean alpha value of the ICU total and subscale scores were acceptable, ranging from .70 (unemotional subscale) to .81 (total score). Moderator analyses indicated that the mean and standard deviation of the total scores, age group, and administration format accounted for 35.51% of the total variability of the alpha values. The observer-report version had substantially higher reliability than the self-report version. We discuss the implications of these findings for future clinical research and practice. (PsycINFO Database Record (c) 2019 APA, all rights reserved).