INTRODUCTION: Black men who have sex with men (MSM) and women but who do not identify as gay or disclose their bisexual activities to main female partners, also known as men "on the down-low," have been cited as the main reason for the increase in HIV infections in black women. METHODS: Three online databases (PsychInfo, MEDLINE and AIDSLINE) were searched for scientific articles related to men on the down-low. A total of 24 articles and two conference abstracts were selected for review. RESULTS: Data from existing studies of MSM reveal low agreement between professed sexual identity and corresponding sexual behavior among black and other MSM; show that black MSM are more likely than MSM of other racial or ethnic groups to be bisexually active or identified; and, compared with white MSM, are less likely to disclose their bisexual or homosexual activities to others. However, black MSM who do not disclose their homosexual or bisexual activities engage in a lower prevalence of HIV risks than black MSM who do disclose; and black men who are currently bisexually active account for a very small proportion of the overall population of black men (2%). CONCLUSION: The high prevalence of HIV in the black community and the greater likelihood of bisexuality among black men place heterosexual black women at risk for HIV infection. However, the contribution of high-risk heterosexual black men to the rising HIV caseload among black women has been largely ignored. Future research must evaluate the relative contributions of bisexual men and exclusively heterosexual black men to HIV cases among black women.