Empirical investigation into disruptive behavior disorders (DBDs) and attention deficit/hyperactivity disorder (ADHD) in early childhood has expanded considerably during the past decade. Although there have been considerable gains in the understanding of the presentation and course of these psychiatric disorders in early childhood, the lack of a developmental framework to guide nosologic issues likely impedes progress in this area. The authors propose that enhanced developmental sensitivity in defining symptoms of DBDs and ADHD may shed light on outstanding issues in the field. In particular, developmental specification may enhance specificity, sensitivity, and stability of DBDs and ADHD symptoms as well as inform our understanding of which type of treatment works best for whom. This article provides an overview of these critical issues.