This paper reviews several attempts to extend the construct of psychopathy to children and adolescents. The research suggests that the presence of callous-unemotional (CU) traits may be particularly important. Specifically, the presence of these traits designates a clinically important subgroup of youth with childhood-onset conduct problems who show a particularly severe, aggressive, and stable pattern of antisocial behaviour. Also, children with CU traits show numerous emotional, cognitive, and personality features that are distinct from other antisocial youth that are similar to features found in adults with psychopathy. The research on CU traits has important implications for understanding the different causal pathways through which children develop severe antisocial and aggressive behaviour, as well as implications for diagnosing and intervening with antisocial youth.