Background:  In New York City (NYC), the majority of new HIV diagnoses in women are due to heterosexual transmission, though the specific risk of partners is rarely known or reported. Of men who have sex with men (MSM) who are living with HIV/AIDS in NYC, 12% also report sex with women. They may serve as a bridge population for HIV transmission to women. We hypothesize that a significant proportion of bisexual men engage in high-risk sex with both men and women.

Methods:  The HIV Testing Survey (HITS) is an anonymous behavioral risk survey of populations at risk for HIV. In 2000 and 2002, we interviewed 363 men at 5 gay bars in NYC. The interview covered sexual behavior with primary and casual male and female partners. We defined bisexual as sex with men and women in the previous 12 months (behaviorally bisexual) or self-identification as bisexual. We defined high-risk sex with men as unprotected receptive or insertive anal sex or multiple male partners (4 or more in the previous 12 months), and high-risk sex with women as unprotected vaginal or anal sex or multiple female partners.

Results:  Among 363 men, 85 (23%) were bisexual. Bisexuality was reported more often in black (34%) and Asian (26%) than in white (12.8%) men (p = 0.02), and in men <35 years old (28%) compared with ≥35 (17%) (p = 0.01). Bisexual men and MSM did not differ only in self-reported HIV⁺ status (13% vs 8%, p = 0.11) or high-risk sex with men (61% vs 52%, p = 0.12). Of the bisexual men, 41 (48%) were behaviorally bisexual. In this group, 15% reported primary male partners only, 63% casual male partners only, and 22% both; in relationships with women, 34% had primary female partners only, 51% casual female partners only, and 15% both. Overall, 56% of the behaviorally bisexual men reported high-risk sexual behavior with men:  70% had 4 or more partners in previous 12 months, 13% unprotected receptive anal or insertive sex with last partner, and 17% both. Among those who had high-risk sex with other men, 52% also had high-risk sex with their female partners.

Conclusions:  In this sample of men recruited from gay bars, bisexuality was prevalent, and almost one third of the behaviorally bisexual men had high-risk sex with both men and women. HIV prevention messages to men and women should acknowledge the intersection of MSM and heterosexual women. Larger and more diverse samples of bisexual men are needed to explore the extent of the HIV risks for both bisexual men and their female partners.

Keywords: women; bisexual