BACKGROUND: Empirical research indicates that high rates of mental health issues in members of marginalised population groups are predicted in part by their decisions to disclose or conceal their stigmatized identities from others-a field of study known as METHODS: This scoping review explores the theoretical and operational definitions of trans disclosure and concealment in 46 English-language papers, identified from extensive database searches, addressing relationships between these concepts and mental health factors. RESULTS: Findings indicate that the issues outlined above remain unresolved, even in the widely-used CONCLUSION: We encourage researchers to address these neglected areas, reevaluate the language used in measurement questions, and conduct longitudinal research to support an accurate understanding of trans outness phenomena.