<p>Oppositional defiant disorder (ODD) has been linked to emotion dysregulation, but longitudinal studies are lacking. This study aimed to assess the trajectories of emotion regulation, lability/negativity and ODD symptoms in a longitudinal study, with three time points, including two separate school levels (preschool and elementary school) and separately for boys and girls. Parents and teachers completed the Emotion Regulation Checklist, the Disruptive Behavior Rating Scale and the ADHD Rating Scale-IV for 620 children, 284 girls (45.8%) and 336 boys (54.2%), ages 5–6 at time 1 (mean age = 5.69, <i>SD</i> =.31), ages 6–7 at time 2 (mean age = 6.61, <i>SD</i> =.30) and ages 7–8 at time 3 (mean age = 7.60, <i>SD</i> =.30). The results from cross-lagged panel models suggest that emotion regulation, lability/negativity and ODD symptoms are strongly related and co-developed over time, both according to parents and teachers. The growth curve models also implied the predictive element of emotion dysregulation for ODD symptoms but the cross-lagged panel models did not which should caution any interpretation. The findings of this study suggest that emotion dysregulation might be considered a characteristic or feature of ODD symptoms rather than a risk factor, given that the results from the cross-lagged panel models show a stronger pattern of co-development rather than prediction and also showed that higher levels of ODD symptoms predicted worse emotion regulation and higher lability/negativity.</p>