Recent research has indicated that deviant peers may play a role in cognitive development. This is particularly the case for the dual systems model, a key framework for understanding engagement in antisocial behavior during adolescence and emerging adulthood. However, limited research has examined how preexisting mental health concerns may moderate these relationships. This study used the Pathways to Desistance data to examine attention deficit hyperactivity disorder (ADHD) as a moderator of the relationships between deviant peer association and dual systems model constructs. Generalized estimating equations were used to test these relationships. Results indicated that deviant peer association and the presence of ADHD both predicted increased sensation-seeking and lower impulse control. ADHD significantly moderated the relationship between deviant peer association and impulse control, indicating a weaker impact of deviant peer association on impulse control among participants with ADHD. No significant interaction was observed for the relationship between deviant peer association and sensation-seeking.