Bisexual behaviors may increase transmission pathways of HIV and sexually transmitted infections (STIs) from a higher prevalence group to lower prevalence groups in El Salvador. In 2008, men who have sex with men (MSM) were recruited in San Salvador and San Miguel using respondent driven sampling. Participants were interviewed and tested for HIV and STIs. Sixteen seeds and 797 MSM participated; 34.9% in San Salvador and 58.8% in San Miguel reported bisexual behavior. Bisexual behavior was associated with drug use (adjusted odds ratio (AOR) = 2.57, 95% CI: 1.30-5.06) and insertive anal sex (AOR = 5.45, 95% CI: 3.01-9.87), and inversely associated with having a stable male partner (AOR = 0.47, 95% CI: 0.26-0.84) and disclosing MSM behavior to family (AOR = 0.41, 95% CI: 0.22-0.75). Bisexual behavior was associated with risk behaviors with male and female partners that may be associated with HIV and STI transmission. Bisexual men displayed a distinct identity calling for tailored interventions.