Studies show interpersonal callousness (IC) plays an important role in understanding persistent antisocial behaviors; however, it remains unclear whether IC is a unidimensional construct, represented by invariant behavioral indexes and stable across different developmental periods. This study explores the structure and stability of IC using parent and teacher reports of IC behaviors in a cohort of 506 inner-city boys assessed annually from ages 8 to 16. Results support the unidimensionality of the IC construct from childhood to adolescence and reveal longitudinal invariance between ages 8 to 11 and 12 to 16 in the case of parent report and from age 11 to 16 in the case of teacher report. Findings reveal significant stability of IC across 9 years of assessment. This study emphasizes the importance of testing the longitudinal invariance of constructs that span multiple developmental periods to promote a more unambiguous understanding of developmental stability and change.