Mistrust of health care providers among persons of color is a significant barrier to engaging them in research studies. Underrepresentation of persons of color is particularly problematic when the health problem under study disproportionately affects minoritized communities. The purpose of this study was to test the validity and reliability of an abbreviated and adapted version of the Group Based Medical Mistrust Scale. The GBMMS is a 12-item scale with three subscales that assess suspicion, experiences of discrimination, and lack of support in the health care setting. To adapt for use in the research setting, we shortened the scale to six items, and replaced "health care workers" and "health care" with "medical researchers" and "medical research," respectively. Using panelists from a market research firm, we recruited and enrolled a racially and ethnically diverse sample of American adults (N = 365) and adolescents aged 14-17 (N = 250). We administered the adapted scale in a web-based survey. We used Cronbach's alpha to evaluate measure internal reliability of the scale and external factor analysis to evaluate the relationships between the revised scale items. Five of the six items loaded onto a single factor, with (α = 0.917) for adolescents and (α = 0.912) for adults. Mean scores for each item ranged from 2.5-2.9, and the mean summary score (range 6-25) was 13.3 for adults and 13.1 for adolescents. Among adults, Black respondents had significantly higher mean summary scores compared to whites and those in other racia/ethnic groups (p<0.001). There was a trend toward significance for Black adolescents as compared to white respondents and those in other racial/ethnic groups (p = 0.09). This five-item modified version of the GBMMS is reliable and valid for measuring research mistrust with American adults and adolescents of diverse racial and ethnic identities.