The purpose of this study was to investigate reasons HIV-positive gay men give for disclosing or not disclosing their serostatus to their casual sexual partners. Participants were 78 HIV-positive gay men who were part of a larger HIV and disclosure project. A clear factor structure for disclosure emerged which suggests that issues of responsibility dominated men's decisions to disclose. No clear factor structure for nondisclosure emerged. Reasons for disclosure or nondisclosure to casual sexual partners were varied and this data could provide new insights for secondary prevention efforts. More research needs to be conducted to better understand salient issues in considering whether to disclose.