Objective: Emotional lability (EL) and oppositional defiant disorder (ODD) frequently co-occur with ADHD. This study evaluates whether EL merely represents the negative “mood/affect” component of ODD or forms a distinct dimension. Method: EL and ODD data from 1,317 ADHD participants were analyzed using exploratory factor analysis (EFA) and confirmatory factor analysis (CFA) for binary data. Results: Within ADHD, 39.4% children had ODD and 42.6% had EL. A sizable proportion expressed only either ODD or EL: 16.6% had ODD-only, 19.7% had EL-only, and 22.9% expressed both. In both EFA and CFA, EL forms a separate dimension from ODD items and the “mood/affect” subdimensions (whether classified by Diagnostic and Statistical Manual of Mental Disorders [5th ed.; DSM-5] or the Burke et al. models or the de novo ODD subdimensions derived from our data). This factorial structure remains invariant across gender. Conclusion: EL is distinct from ODD and its “mood/affect” subdimensions. In line with emerging evidence, our findings provide further evidence of factorial validity for EL as a separate construct from ODD.