Objective: To test the previously suggested hypothesis that those with comorbid ADHD and Conduct Disorder (CD) diagnoses differ from other antisocially involved youth in terms of higher rates of violent behavior, impulsiveness, and psychopathic traits. Method: Three hundred eighty juvenile incarcerated delinquents from Northern Russia were assessed by means of semi-structured psychiatric interview and by student and teacher self-reports. Results: The study has demonstrated higher rates of psychiatric disorders and of comorbidity, as well as more complicated substance abuse and disruptive behaviors in those with combined ADHD–CD diagnosis, as compared with CD only, ADHD only, and no CD no ADHD groups. The results regarding psychopathic traits were inconclusive. Conclusion: The group with combined ADHD–CD diagnosis is more severely disturbed, both as concerns psychiatric comorbidity and more severe aggressive and disruptive behaviors. However, there is only limited evidence supporting a higher prevalence of psychopathic traits in this group.