The link between oppositional defiant disorder (ODD) and conduct disorder (CD) was evaluated in 140 children with attention-deficit hyperactivity disorder (ADHD) and 120 normal controls examined at baseline and 4 years later, in midadolescence, at the Pediatric Psychopharmacology Unit, Psychiatric Service, Massachusetts General Hospital, Boston, MA. Of ADHD children, 65% had comorbid ODD and 22% had CD at baseline. Of ODD children, 32% had comorbid CD. Children with CD also had ODD that preceded CD by several years. Children with both ODD and CD had more severe symptoms of ODD, more psychiatric disorders, more bipolar disorder, and more abnormal behavior scores compared to ADHD children without comorbidity. Risk of CD at 4-year follow-up was not increased in children with ODD without CD at baseline. Two subtypes of ODD associated with ADHD were evident: one prodromal to CD and one that is not. 
COMMENT. The majority of ODD children with ADHD do not have comorbid CD, whereas CD is almost always comorbid with ODD which precedes the onset of CD by several years. The majority of children with ADHD and CD had developed CD before age 12 years. Adolescent onset CD is rare. CD with ADHD is associated with higher frequency of substance abuse in adolescence, and higher levels of anxiety disorders and mood disorders. Two ODD subtypes, one prodromal to CD and one without, have different outcomes.