Men who have sex with men (MSM) who are on the "down low" (DL) have been the subject of considerable media attention, but few data on this population exist. This exploratory study (N=455) compared MSM who considered themselves to be on the DL with MSM who did not (non-DL MSM). 20% self-identified as DL. Blacks and Hispanics were more likely than Whites to self identify as DL. MSM who did not identify as gay were more likely than gay-identified MSM to describe themselves as DL. DL-identified MSM were less likely to have had seven or more male partners in the prior 30 days, but were more likely to have had a female sex partner and to have had unprotected vaginal sex. DL-identified MSM were less likely to have ever been tested for HIV than were non-DL MSM. Prevention agencies should expand existing programs for MSM to include specific efforts to reach DL MSM.