OBJECTIVE: To investigate the associations between mental health literacy (MHL), self-disclosure and psychological distress among HIV-positive young and middle-aged men who have sex with men (MSM). We hypothesised that self-disclosure would mediate the relationship between MHL and psychological distress. DESIGN: A cross-sectional study. SETTING: Participants were recruited from the outpatient clinic of the Department of Infection at a tertiary hospital in Nanjing, Jiangsu province, China. PARTICIPANTS: A total of 209 HIV-positive young and middle-aged MSM. OUTCOME MEASURES: Using convenient sampling method, the study selected 209 HIV-positive young and middle-aged MSM from a tertiary hospital in Nanjing, China, from November 2023 to January 2024. The data were collected using a general information questionnaire, the Multicomponent Mental Health Literacy, the Kessler Psychological Distress Scale and the Distress Disclosure Index. Descriptive statistics, Pearson correlation analysis and mediation analysis were conducted in the study. RESULTS: The mean MHL score among HIV-positive young and middle-aged MSM was 11.90 (SD=5.09). Their mean score for self-disclosure was 31.97 (SD=6.87) and for psychological distress was 25.43 (SD=8.16). The bivariate correlation analysis showed that self-disclosure was positively correlated with MHL (r=0.264, p<
0.001) and negatively correlated with psychological distress (r=-0.496, p<
0.001), and MHL was negatively correlated with psychological distress (r=-0.308, p<
0.001). Self-disclosure partially mediated the relationship between MHL and psychological distress among HIV-positive young and middle-aged MSM, and the mediating effect accounted for 38.31% of the total effect. CONCLUSION: Self-disclosure mediated the relationship between MHL and psychological distress. To improve psychological distress among HIV-positive young and middle-aged MSM, targeted intervention measures aimed at enhancing MHL and self-disclosure should be conducted.