This study aimed to refine the ADHD phenotype by examining impulsivity and emotional dysregulation through behavioral and trait-based measures in 844 children, using both cross-sectional and longitudinal analysis. The results identified two key factors—Undercontrol (including hyperactivity, impulsivity, and low behavioral regulation) and Emotional Dysregulation (including negative emotionality, irritability, and low ego-resiliency)—that were strongly linked to ADHD and other psychiatric conditions. Longitudinally, the Undercontrol factor predicted worsening ADHD symptoms, the onset of new disruptive disorders, and suicidal thoughts, while Emotional Dysregulation was associated with lower likelihood of marijuana use. The study supports a dimensional approach to ADHD that could improve clinical assessment and outcomes.