PURPOSE: Disruptive behavior disorders (DBD) and attention-deficit/hyperactivity disorder (ADHD) are externalizing disorders that frequently co-occur but also have distinct clinical characteristics. Identifying distinct neurocognitive phenotypes may help optimizing individual diagnosis and treatment of both disorders.

METHODS: Using data from 6,517 children and adolescents from the Philadelphia Neurodevelopmental Cohort, we investigated diagnostic group (i.e., typically developing, DBD, ADHD, DBD + ADHD) and sex differences across various neurocognitive functions, as well as co-occurring psychiatric symptoms, while adjusting for various confounding factors.

RESULTS: Neurocognitive deficits were associated with ADHD but not DBD. Co-occurring DBD in both girls and boys with ADHD did not appear to have an additive deteriorating effect on neurocognitive functioning. Task-specific sex differences were observed but did not interact with diagnostic group.

CONCLUSIONS: The findings of this study suggest that neurocognitive deficits in DBD seem to be largely driven by co-occurring ADHD and this applies equally to both sexes.