Objective: Oppositional defiant disorder (ODD) is classified as a disruptive disorder, but shows a wide range of associations with other psychopathology, including internalizing problems. The reasons for these associations are unclear. Here we test the hypothesis that two distinct early temperamental precursors--emotionality and activity--underlie ODD and differentially predict its comorbidities. Method: The Avon Longitudinal Study of Parents and Children (ALSPAC) community-based representative sample was used. Temperamental dimensions at the age of 38 months were derived through exploratory factor analysis from the Emotionality Activity Sociability (EAS) scale and used in logistic regression predicting to psychiatric diagnoses at the age of 91 months. Results: Pure ODD was predicted by both emotionality (relative risk ratio [RRR] = 1.34, CI = 1.09 to 1.66) and activity (RRR = 1.39, CI = 1.07 to 1.81). The strongest predictions were from early temperament to ODD with comorbidity: from emotionality to ODD plus internalizing disorders (RRR = 3.33, CI = 2.14 to 5.19), and from activity to ODD plus ADHD (RRR = 3.24, CI = 1.48 to 7.11). Temperamental activity was a predictor of the hyperactive-impulsive and combined types of ADHD but not of the inattentive type. Conclusions: Classified as a disruptive disorder, ODD is predicted by early emotion dysregulation as well as by high levels of temperamental activity. The findings of this study suggest that early emotionality and activity differentially contribute to the phenotype of ODD in middle childhood and may determine its range of co-occurrence with other psychopathology. Taking into account the heterogeneous origins of childhood oppositionality may help to refine clinical approaches to ODD. (Contains 1 figure and 3 tables.)