The current study considers methodological challenges in developmental research with linguistically diverse samples of young adolescents. By empirically examining the cross-language measurement equivalence of a measure assessing three components of ethnic identity development (i.e., exploration, resolution, and affirmation) among Mexican American adolescents, the study both assesses the cross-language measurement equivalence of a common measure of ethnic identity and provides an appropriate conceptual and analytical model for researchers needing to evaluate measurement scales translated into multiple languages. Participants are 678 Mexican-origin early adolescents and their mothers. Measures of exploration and resolution achieve the highest levels of equivalence across language versions. The measure of affirmation achieves high levels of equivalence. Results highlight potential ways to correct for any problems of nonequivalence across language versions of the affirmation measure. Suggestions are made for how researchers working with linguistically diverse samples can use the highlighted techniques to evaluate their own translated measures. (Contains 5 tables.)