Objective-The purpose of the current study was to assess whether or not men who have sex with men who limit their unprotected anal sexual partners to those who are of the same HIV status (serosort) differ in their risk for HIV transmission than MSM who do not serosort.Methods-Cross-sectional surveys administered at a large gay pride festival (80% response rate) were collected from MSM. Univariate and multivariate logistic regressions were used to identify predictors of serosorting.Results-Participants were self-identified as HIV negative MSM (N=628), about one third of whom engaged in serosorting (n=229). Men who serosort were more likely to believe that serosorting offered protection against HIV transmission, perceived themselves as being at no relatively higher risk for HIV transmission, and had more unprotected anal intercourse partners. Over half the sample reported their frequency of HIV testing as yearly or less frequently; this finding did not differ between serosorters and non-serosorters.Conclusions-Men who identify as HIV negative and serosort are no more likely to know their HIV status than men who do not serosort and are at higher risk for exposure to HIV. Interventions targeting MSM must address the limitations of serosorting.Human Immunodeficiency Virus (HIV) is the most destructive pandemic in history, with nearly 40 million people worldwide living with HIV 1 . In the US it is estimated that one million people are infected with HIV and there are over 40,000 new HIV infections in the US each year, the majority of which occur among men who have sex with men 2 . To reduce the likelihood of HIV transmission, many individuals seek out their own strategies of prevention. One such method is serosorting; the practice of limiting sexual partners to those who have the same HIV serostatus. Several studies have found that serosorting is commonly used among men who have sex with men 3-6 . For many HIV infected and uninfected persons, serosorting is believed to reduce concerns about HIV/AIDS and make condom use less necessary. Additionally, for various reasons, people tend to dislike using condoms [7][8][9] and practice behaviors they believe are protective, such as serosorting, to avoid condom use. Public health policy is also embracing serosorting as a viable alternative to condom use. 10 As a result, partner HIV serostatus is often a determining factor in sexual risk decision making. 11,12 Multiple caveats to serosorting do exist. For uninfected persons, the effectiveness of serosorting relies on complete and open HIV status disclosure among monogamous men. Unfortunately, fear of rejection, physical threat, alcohol or drug related impairment, and the lag between HIV tests can all affect the accuracy of knowing a sexual partner's HIV status. Moreover, HIV testing is not universal among men who have sex with men (MSM). 13 16 In light of these circumstances, serosorting may be limited for preventing HIV transmission.Beliefs about the protective benefits of serosorting are inextricably linked to risk per...