This study tested the hypothesis that attention-deficit/hyperactivity disorder (ADHD) and conduct disorder (CD) comorbidity is associated with substance use and deviance severity in 395 adolescents with alcohol use disorder. Thirty percent of the adolescents had high ADHD symptom counts, and 73% had 3 or more CD symptoms. ADHD-CD was associated with nonalcohol substance use disorder, drinking levels, and CD severity, but in general substance use was not uniquely elevated or problematic among the comorbid cases. In general, CD and CD severity were more important. The findings did not differ between boys and girls, revealing that in a treatment sample of adolescents, ADHD-CD comorbidity may need to be assessed and treated, but it is not broadly indicative of severity.