Sexual orientation disclosure has been shown to be associated with sexual risk behaviors (SRBs) and HIV infection among gay men. However, most previous studies are based on a cross-sectional design without a control group and do not distinguish between the subjects of disclosure. This study aimed to explore the impact of sexual orientation disclosure to parents on SRBs and HIV infection over 15 years. We conducted a longitudinal case-control study with 648 gay men who disclosed their sexual orientation to their parents and 648 who did not, all from Changsha, China. Data were collected at baseline in 2009 and at follow-up in 2024, focusing on five types of SRBs and HIV infection status. Generalized linear models were used to assess the impact of disclosure at baseline on SRBs and HIV infection at follow-up. The results showed that the disclosure group was less likely to have SRBs, including CAS (Risk Ratio [RR]: 0.61, 95% Confidence Interval [CI] 0.51-0.73), multiple concurrent sexual partners (RR: 0.74, 95% CI 0.62-0.88), group sex (RR: 0.64, 95% CI 0.51-0.81), chemsex (RR: 0.71, 95% CI 0.52-0.96), and commercial sex (RR: 0.54, 95% CI 0.42-0.70). They were also less likely to be infected with HIV (RR: 0.78, 95% CI 0.64-0.94). The study underscores the importance of sexual orientation disclosure in reducing the risk of SRBs and HIV infection among gay men, with significant implications for informing future public health policies and interventions for HIV prevention.