Objective: In nationally funded research in the U.S., ethnicity and race are measured with checkbox questions, the limited categories of which may yield significant missing data and low salience to available categories, particularly among adults of color. How adolescent-generated data compare to these limited categories, and how adolescents, not just those of color, describe their culture are understudied. In our sample, we asked the following: (a) how do adolescents' ethnicity/race and culture identifications compare?, (b) how do adolescents' open-ended ethnicity/race and checkbox ethnicity/race labels compare?, and (c) how do adolescents' ethnicity/race labels compare to available categories for identification on the National Institutes of Health's (NIH's) demographic form? Method: Data from 76 adolescents (64.5% female, M age = 15.78 years) were qualitatively and quantitatively analyzed. Results: White adolescents were as likely as adolescents of color to identify with cultural labels, and most adolescents described culture differently than race/ethnicity. White adolescents' open-ended and checkbox labels overlapped more (38.8%) than adolescents of colors' (22.5%). Only 17% of adolescents' open-ended race/ethnicity identification labels and 54% of their checkbox identifications were available on the NIH's demographic form. Conclusions: As measurement of demographic data is reduced to few options that favor privileged identities, innovative methods to measure individuals' identities are warranted. Using tools that do not reflect individuals' identity labels may increase error and reflects structural problems of research inequity. Our findings provide initial evidence of this methodological issue in a sample of adolescents. Building inclusive demographic tools from individuals' self-descriptors that remain feasible and practical for use can diminish inequity associated with describing "diverse" populations. Public Significance Statement This study provided support for measuring culture and expanding ethnicity/race reporting categories using individuals' own labels in a sample of ethnic/racially diverse adolescents. As limited-category ethnicity/race measurement forms favor privileged identities, we provide support for adapting them to be more inclusive and valid in representing an increasingly diversifying population.