This study sought to explore an online intervention that was initiated by an AIDS service organization to reduce sexual risk within a geographically-oriented chat room frequented by men who have sex with men (MSM). Analyses of bio lines, user profiles, and chat room discussions were used to understand and characterize the online prevention intervention. Six predominate discussion topics were identified, including (a) sexual risk reduction strategies (e.g., safer "barebacking"), (b) HIV testing options, (c) local alternatives for nonsexual social support, (d) referrals for youth, (e) resources related to "coming out," and (f) access to risk reduction materials and supplies. The perceived anonymity promoted by the Internet and the health educator's established relationship with the men in the chat room contributed to the success of this intervention. This analysis suggests that an online HIV/AIDS prevention intervention may reach MSM inaccessible in traditional venues typically used for intervention delivery.