In DSM 5, conduct disorder (CD) has been expanded with a new specifier ‘with Limited Prosocial Emotions’ (LPE) in addition to the age-of-onset (AoO) subtyping, and is thought to identify a severe antisocial subgroup of CD. However, research in clinical practice has been scarce. Therefore, the current study will examine differences in clinical symptoms between subtypes of CD, based on both subtyping schemes. Subsequently, it will investigate whether the LPE specifier explains unique variance in aggression, added to the AoO subtyping. A sample of 145 adolescents with CD (51 % male, mean age 15.0) from a closed treatment institution participated in this study. CD diagnoses and AoO subtype were assessed using a structured diagnostic interview. The LPE specifier was assessed using the callous–unemotional dimension of the Youth Psychopathy Traits Inventory (YPI). Self-reported proactive and reactive aggression, rule-breaking behavior and internalizing problems within the subtypes were compared. Youth with childhood-onset CD and LPE showed significantly more aggression than adolescent-onset CD without LPE (proactive aggression: F = 3.1, p < 0.05, reactive aggression: F = 3.7, p < 0.05). Hierarchical regression revealed that the LPE specifier uniquely explained 7 % of the variance in reactive aggression, additionally to the AoO subtyping. For proactive aggression, the interaction between AoO and the LPE added 4.5 % to the explained variance. Although the LPE specifier may help to identify a more aggressive subtype of CD in adolescents, the incremental utility seems to be limited. Therefore, clinical relevance of the LPE specifier in high-risk adolescent samples still needs to be investigated thoroughly.