The aim of this study was to examine online profile and in-person communication patterns and their associations with unprotected anal intercourse (UAI) in online and offline partnerships between men who have sex with men (MSM) who have never tested for HIV ("Never Tested"), had been tested at least once for HIV ("Tested"), and had tested positive for HIV. Between September and November 2005, 2,716 MSM participated in a one-time online survey. Although 75% and 72% of the Tested and Never Tested groups disclosed a HIV-negative status in all of their online profiles, 17% of HIV-positive participants did so. Exchanging HIV status information was highest among the Tested group, while HIV-positive men were most likely to negotiate UAI. Serodisclosure was not an independent predictor of UAI, although making an explicit agreement to engage in UAI was. Sexual communication and risk-taking patterns differed by testing status. Explicit agreements to avoid UAI were associated with reduced sexual risk-taking. Misrepresentation of HIV status is an identified challenge for HIV prevention.