Over the past 15 years, three distinct models have been used to characterize the factor structure of attention deficit hyperactivity disorder (ADHD). These models correspond to descriptions of the disorder as outlined in DSM-III, DSM-III-R, and now, DSM-IV. Specifically, in DSM-III, inattention, impulsivity, and hyperactivity were treated as three separate constructs. In DSM-III-R, ADHD was treated as a unitary construct. In DSM-IV, impulsivity and hyperactivity remain combined, but inattention is considered a separate construct. The present study examined and compared each of these models using confirmatory factor analyses. A final set of comparisons was conducted examining ADHD symptoms together with oppositional defiant disorder/conduct disorder (ODD/CD) symptoms. Although support for the three-factor ADHD model (DSM-III version) was obtained when the ADHD symptoms were examined in isolation, the two-factor model of ADHD (DSM-IV version) was supported when ADHD and ODD/CD symptoms were examined together as part of a comprehensive model of disruptive behavior disorders.