Both population based surveys and more focused research studies indicate that increased numbers of sexual partners and partner concurrency contribute to increased risk for acquisition of sexually transmitted infection (STI), including HIV infection. However, unlike for men, both national and sub-population-based studies consistently find that the great majority of women with or without STIs report only 1-2 sex partners in the preceding year and that a minority of women acknowledge > 3 sex partners over the same period, suggesting that this relatively small proportion of women with higher numbers of sex partners play a disproportionate role in sustaining community STI rates. Despite these observations, surprisingly little is known about women with increased numbers of sexual partners, the factors which contribute to increased partner number, and the potential for those factors to be intervened upon to reduce risk for STI. The implications of these facts for STI/HIV prevention efforts are profound. For instance, interventions that include the implication that target audiences have multiple sex partners might be dismissed as irrelevant by those with single partners. Conversely, interventions targeting women with multiple sex partners may be based on assumptions derived from data which, while representative of the general target audience, may not reflect relevant circumstances for the subset of women with higher numbers of partners.