The sexual behaviors of non-gay identified men who have sex with men and women (MSMW) who do not disclose their same-sex behavior to their female partners (referred to by some as men “on the down low”) were examined, including the potential for these men to serve as a “bisexual bridge” for HIV and STD acquisition and transmission. Self-reported sexual behavior data were collected as part of an exploratory study of an ethnically diverse (41% African American, 35% Latino, 22% White, and 2% Asian) sample of 46 non-gay identified, non-disclosing MSMW in New York City. Men reported significantly more male than female sexual partners, but more frequent sex with females. The prevalence and frequency of unprotected sex did not differ significantly between male and female partners in the past 3 months. Men reported risk behavior more often with steady female and steady male partners (e.g., wives, girlfriends, boyfriends) than with more casual male and female partners (regular uncommitted partners, one-night stands). Men, especially African American/Black men, were significantly less likely to report receptive sexual behaviors with men than insertive behaviors. Unprotected sex was common with male and female partners in the past 3 months (e.g., 35% of anal sex with men; 50% of vaginal sex). Indeed, 22% of the sample (38% of those who had both recent males and female partners) reported both unprotected vaginal sex and unprotected anal sex with a male partner during the past 3 months. Although the study was limited by a small convenience sample, the findings suggest that non-gay identified non-disclosing MSMW are at risk for the acquisition and transmission of HIV and STDs, and may serve as a potential bridge, suggesting the need for further research and intervention targeting this unique population.