Objectives To examine gay men's patterns of self-disclosure of HIV seropositivity to friends, lovers, relatives and colleagues; to assess the effects of disclosure; and to identify reasons for not disclosing to particular individuals. Design Longitudinal questionnaire survey of gay men. Methods A total of 163 HIV-positive men participating in the AIDS Behavioral Research Project, a longitudinal study of San Francisco gay men, completed questionnaires about their self-disclosure patterns, health status, and psychological well-being. Results HIV-positive men were most likely to disclose their status to lovers and closest gay friends. Asymptomatic men were less likely to disclose to relatives and colleagues than symptomatic men. Friends and lovers were rated as responding more helpfully than relatives and colleagues. Men who perceived their significant others as responding more helpfully were less depressed and anxious currently and 1 year later. A variety of reasons were given for not disclosing, including not wanting to worry others, fear of discrimination, fear of disrupting relationships, and emotional self-protection. Conclusion While disclosure can have advantages for both HIV-positive individuals and their significant others, HIV-positive individuals must be assured that the benefits of doing so will outweigh the potential costs.