The purpose of the study was to determine the potential contribution of bisexual men to the spread of HIV in Los Angeles. We compare the characteristics and behaviors of men who have sex with men and women (MSMW) to men who have sex with only women (MSW) and men who have sex with only men (MSM) in Los Angeles. Men (N = 1,125) who participated in one of the two waves of data collection from 2005 to 2007 at the Los Angeles site for NIDA's Sexual Acquisition and Transmission of HIV-Cooperative Agreement Program were recruited using Respondent Driven Sampling. Participants completed Audio Computer Assisted Self Interviews and received oral HIV rapid testing with confirmatory blood test by Western Blot and provided urine specimens for detection of recent powder cocaine, crack cocaine, methamphetamine, or heroin use. MSM, MSW, or MSMW were defined by the gender of whom they reported sex with in the past 6 months. Chi-square tests and ANOVAs were used to test independence between these groups and demographic characteristics, substance use, and sexual behaviors. We fit generalized linear random intercept models to predict sexual risk behaviors at the partner level. Men were mostly of low income, unemployed, and minority, with many being homeless; 66% had been to jail or prison, 29% had ever injected drugs, and 25% had used methamphetamine in the past 30 days. The sample had high HIV prevalence: 12% of MSMW, 65% of MSM, and 4% of MSW. MSMW were behaviorally between MSW and MSM, except that more MSMW practiced sex for trade (both receiving and giving), and more MSMW had partners who are drug users than MSW. Generalized linear random intercept models included a partner-level predictor with four partner groups: MSM, MSMW-male partners, MSMW-female partners, and MSW. The following were significantly associated with unprotected anal intercourse (UAI): MSW (AOR 0.15, 95% CI 0.08, 0.27), MSMW-female partners (AOR 0.4, 95% CI 0.27, 0.61), HIV-positive partners (AOR 2.03, 95% CI 1.31, 3.13), and being homeless (AOR 1.37, 95% CI 1.01, 1.86). The factors associated with giving money or drugs for sex were MSMW-female partners (AOR 1.70, 95% CI 1.09, 2.65), unknown HIV status partners (AOR 1.72, 95% CI 1.29, 2.30), being older (AOR 1.02, 95% CI 1.00, 1.04), history of incarceration (AOR 1.64, 95% CI 1.17, 2.29), and being homeless (AOR 1.73, 95% CI 1.27, 2.36). The following were associated with receiving money or drugs for sex: MSW (AOR 0.53, 95% CI 0.32, 0.89), African American (AOR 2.42, 95% CI 1.56, 3.76), Hispanic (AOR 1.85, 95% CI 1.12, 3.05), history of incarceration (AOR 1.44, 95% CI 1.04, 2.01), history of injecting drugs (AOR 1.57, 95% CI 1.13, 2.19), and had been recently homeless (AOR 2.14, 95% CI 1.57, 2.94). While overall HIV-positive MSM had more UAI with partners of any HIV status than MSMW with either partner gender, among HIV-positive MSMW, more had UAI with HIV-negative and HIV status unknown female partners than male partners. Findings highlight the interconnectedness of sexual and drug networks in this sample of men-as most have partners who use drugs and they use drugs themselves. We find a concentration of risk that occurs particularly among impoverished minorities-where many men use drugs, trade sex, and have sex with either gender. Findings also suggest an embedded core group of drug-using MSMW who may not so much contribute to spreading the HIV epidemic to the general population, but driven by their pressing need for drugs and money, concentrate the epidemic among men and women like themselves who have few resources.