Measurement invariance (metric/scalar) of oppositional defiant disorder (ODD) dimensions (negative affect, oppositional behavior, and antagonistic behavior) across sex and informants is tested. Parents and teachers of 622 preschool children from the general population answered a dimensional measure of ODD. ODD dimensions function similarly in boys and girls. Some differences were found by informant, indicating that the equivalence of the ratings of parents and teachers is not complete and that given the same underlying level of the latent trait, some parents’ item scores were higher than those of teachers. Metric invariance was complete but scalar invariance was not attained. The results contribute evidence on the conceptualization of ODD as a source-specific disorder. The simultaneous use of ODD dimensions reported by parents and teachers must be considered in the context of a lack of complete measurement invariance, which implies that comparisons of observed means from parents and teachers are not readily interpretable.