1058 transmission risks and a belief that other infected individuals could relate to their experiences: I don’t want to be with someone who’s negative, for two reasons. One, because they don’t know what I’ve been through, and they’ll never understand, and it’s a part of me—again, maybe in a year from now, when it’s not such a big deal […], but not now. Also, I don’t think that I could trust someone, or be 100% with someone, that I could be a threat to. (26 year old gay man, New York) Another participant described a major reduction in partners as well as a new focus on partners who were HIV- positive: Since I’ve been diagnosed, I’ve been back with my steady partner [who is HIV positive]. We’re both pretty open about sex. We’ve played with two other people, both of them also being positive […] It was unprotected. My general attitude I guess is I have the most potentially damaging disease out there. They’re also positive. So I don’t have to worry about giving them HIV. Most other stuff can be cured. (36 year old gay man, San Diego) Learning that Partners Were Already HIV-Positive Although many participants described concerted efforts to serosort after diagnosis, others came to realize all too late that existing partners already were positive: After I got the notice that I was HIV positive, I went back and called everybody that I was playing with. And luckily I found out that half of them were positive […] I called them and I said ‘‘You know what, this is what happened. So I hope you’re doing okay. Go and check yourself.’’ And then some came and said ‘‘Unfortunately I’m positive too.’’ And, you know, I wasn’t shocked but I had to take responsibility for what I had done also. So it was kind of upsetting […] One of the guys came and said ‘‘Well I assumed you were—you knew that I was positive.’’ And I said ‘‘Well how can I assume that you were positive? The last time we talked you told me you have Chlamydia. So if you had something else worse than Chlamydia I was expecting you to tell me.’’ (37 year old gay men, San Francisco) Discussion 123 Our ﬁndings suggest that diagnosis with acute/early HIV infection could play an important role in reducing trans- mission-risk behaviors, but also highlight the need for interventions to enhance and sustain these changes. After AIDS Behav (2009) 13:1054–1060 diagnosis with acute/early infection, participants in our study, nearly all of whom were MSM, reduced their number of partners and serosorted, limiting their unpro- tected intercourse to others they believed to be HIV-posi- tive. (Seropositioning, another informal risk reduction strategy, did not appear to be used by our participants.) Although risk reduction efforts have also been observed among people diagnosed at later stages of HIV (DiF- ranceisco et al. 2005; Weinhardt et al. 1999), such changes are especially important for newly infected individuals because of their heightened infectiousness (Cates et al. 1997; Koopman et al. 1997; Pilcher et al. 2004). In our data, partner reduction and serosorting were often driven by a desire to prevent transmitting the virus to other people. This altruistic motivation is encouraging, and offers a likely area of emphasis to sustain behavior change. However, participants were much less successful at increasing condom use. They expressed pronounced dis- comfort and difﬁculties with condoms and, after diagnosis, the majority of reported sex acts remained unprotected. This ﬁnding stands in contrast to studies looking across risk groups, which observed relative increases in safer sex behaviors after diagnosis (DiFranceisco et al. 2005; Weinhardt et al. 1999). The absence of condom-related behavior change among our mostly MSM participants is likely due to serosorting, which our participants described speciﬁcally as an intended risk reduction strategy. This pattern of results is similar to those of Gorbach and col- leagues (2006), who also observed increased serosorting but no increase in condom use among newly infected MSM, but is different than the ﬁndings of Colfax and colleagues (2002), who documented a decrease in unpro- tected anal intercourse but no shift toward serosorting. Clearly, consistent condom use is the ideal form of trans- mission-risk prevention. But, if a person is unable or unwilling to use condoms, serosorting offers a potential strategy for lowering the chances of HIV transmission. However, its success requires accurate assessments of partners’ serostatuses (Butler and Smith 2007; Pinkerton 2008). Although we do not know exactly how participants determined their partners’ serostatuses, the accuracy of these assessments was almost certainly less than perfect. Only six participants reported engaging in risk behaviors with a person whom they knew to be HIV-positive in the months immediately prior to diagnosis, even though 100% (by deﬁnition) must have done so. And some participants noted explicitly that they learned after diagnosis that their ongoing sexual partners were in fact positive. Thus, it is likely that the pronounced post-diagnosis shift to sero- sorting was driven at least in part by changes in perception. That is, partners previously thought to be HIV-negative or of unknown serostatus were subsequently reclassiﬁed