IntroductionTransgender, gender diverse, and non-binary (TGDNB) adults experience poorer mental health than cisgender peers and access health services to a greater extent. However, they experience a range of minority stress-related barriers to accessing services, such as healthcare discrimination, that are likely to undermine their mental health. The present study examined the effects of healthcare discrimination on mental health outcomes and tested whether TGDNB-specific minority stressors (i.e. nondisclosure and gender dysphoria) mediated these effects.MethodsParticipants were 1156 TGDNB adults (Mage = 23.69, SD = 7.72) from the USA and Australia who completed measures of healthcare discrimination, mental health, gender dysphoria, and nondisclosure in 2018.ResultsAlmost a quarter of participants had experienced healthcare discrimination within the past year. Healthcare discrimination predicted greater psychological distress and suicidality, and these associations were mediated by nondisclosure and gender dysphoria. Specifically, healthcare discrimination predicted greater psychological distress via nondisclosure, gender dysphoria, and the serial path via nondisclosure through gender dysphoria. Healthcare discrimination was also associated with greater suicidality via gender dysphoria and the serial path via nondisclosure through gender dysphoria.ConclusionsTGDNB people experience healthcare discrimination at high rates, and these experiences undermine their mental health. Results highlight the importance of healthcare discrimination, nondisclosure, and gender dysphoria, each of which represent modifiable factors that healthcare practitioners may target to improve mental health outcomes for TGDNB people.Policy ImplicationsFuture directions and implications are discussed in the context of public health policy considerations including anti-discrimination legislation and regulatory requirements for healthcare practitioners.