Sexual partner concurrency plays an important role in HIV and STD transmission. The shortage of African-American men may facilitate partner concurrency. This study evaluated whether the male-to-female ratio was associated with African-American participants' number of recent sexual partners, and whether this association differed by gender. Multilevel modeling was used to determine the influence of individual (i.e., gender) and population-level (i.e., sex ratio) variables on the number of recent sexual partners. African-American patients (N = 915; 52% male) were recruited from an STD clinic. Patients reported their number of sexual partners; the male-to-female ratio per census tract was obtained from the U.S. Census Bureau. There were fewer men than women in nearly all census tracts. The interaction between gender and the male-to-female ratio was significant. For men, there was no association between the sex ratio and their number of sexual partners. For women, as the sex ratio increased, their number of sexual partners increased; however, this association was driven by participants who reported trading sex. We found no evidence that fewer African-American men in a census tract was associated with men having more sexual partners.