Abstract Background The relationship between HIV serostatus disclosure and sexual risk behavior is inconsistent across studies. As men who have sex with men (MSM) are emerging as the key affected population in Bangkok, Thailand with reported HIV prevalence of 30%, we assessed whether HIV disclosure is associated with protected sex in this population. Methods A risk behavior questionnaire was administered using Audio Computer-Assisted Self-Interviewing (ACASI) to determine whether HIV serostatus disclosure was associated with protected sex in 200 HIV-positive MSM in Bangkok. HIV serostatus disclosure to the most recent sexual partner prior to or at the time of the sexual encounter was assessed. Protected sex was defined as insertive or receptive anal intercourse with a condom at the most recent sexual encounter. Results The mean age was 30.2 years, CD4 was 353 cells/mm3, and one-third was on antiretroviral therapy. At the most recent sexual encounter, HIV serostatus disclosure rate was low (26%); 60.5% of subjects had not discussed their serostatus at all, while 5.5% had not revealed their true serostatus. Seventeen percent reported unprotected anal intercourse and about half had sex with their primary partners. The serostatus of the most recent sexual partner was HIV-positive in 19.2%, HIV-negative in 26.4%, and unknown in 54.4% of subjects. There was no association between disclosure and protected sex, with 41 of 48 (85.4%) disclosers and 104 of 126 (82.5%) of non-disclosers reported protected sex (p = .65). Subjects with HIV-positive partners were less likely to report protected sex overall (20 of 33, 60.6%) compared to those with HIV negative (82 of 96, 85.4%) or unknown (41 of 45, 91.1%) partners (p = .001). Age (27-32 years vs. ≤26 years, p = .008), primary partner status (p < .001), and HIV-positive serostatus of sexual partner (p < .001) were significantly associated with disclosure in the multivariate analyses. Conclusion Rates of HIV disclosure to sexual partners by HIV-positive MSM in Bangkok are low. Despite low rates of HIV serostatus disclosure, most HIV-positive MSM reported protected sex with their partners at risk for infection. Future studies should focus on understanding barriers to disclosure and factors driving risk behavior amongst MSM in Thailand.