Lesbian, gay, and bisexual (LGB) people report poorer mental health than heterosexual people. However, there is heterogeneity in this disparity, and a racial/ethnic minority identity can contribute to this heterogeneity. When studying the intersecting effect of sexual identity and race/ethnicity on mental health, research often limits race/ethnicity categories, often uses adult samples from the U.S., and often uses samples that are not nationally representative. To overcome these limitations, the present study examined racial/ethnic heterogeneity in mental health disparities between heterosexual and LGB people in three nationally representative samples. The samples used were the 2011–2012 Understanding Society (U.K. adults; N = 43,904), the 2015 National Survey on Drug Use and Health (U.S. adults; N = 43,313), and the 2015 Youth Risk Behavior Survey (U.S. adolescents; N = 15,122). Using these samples enabled us to contrast the intersection of sexual identity and race/ethnicity across countries (for adults), and between life phases (in the U.S.). Across all three samples, LGB people—and particularly bisexual people—had a higher risk of impaired mental health than heterosexual people. For U.K. adults and U.S. adults, no intersecting effect of sexual identity and race/ethnicity were found. LGB adolescents of color reported better mental health compared with White LGB adolescents. More specifically, Black LGB adolescents reported better mental health compared to White LGB adolescents. Together, the present study contributes to a better understanding of the heterogeneity in mental health disparities for LGB people. (PsycInfo Database Record (c) 2020 APA, all rights reserved)