Objective. Estimate the prevalence of human immunodeficiency virus (HIV) infection and Treponema pallidum in Argentine female sex workers (FSW), and describe the sociodemographic characteristics of this population group associated with HIV transmission. Methods. A cross-sectional study and convenience sampling were conducted in FSW over 18 years of age in nine Argentine cities from October 2006 to December 2009. A total of 1 255 women participated in this study. A group of FSW was especially trained to invite other women to participate in the workshops and undergo screening for HIV and T. pallidum. Results. The most noteworthy socioepidemiological characteristics of the FSW included a high percentage of sexual abuse, limited condom use with noncommercial sex partners, and a high percentage of violence. HIV prevalence was 2% (25/1 255, 95% confidence interval [95% CI]:1.2-2.8) and T. pallidum prevalence was 22.4% (245/1 094; 95% CI: 19.9-24.9). In the city of La Plata, HIV prevalence in FSW was significantly lower compared to that of other regions of the country (0.3% vs. 2.7%, P < 0.05, respectively). Conclusions. The lower HIV prevalence and the higher rate of condom use reported by the women from La Plata surveyed suggest that the presence of a health center for FSW has a direct influence on reducing risky behavior and, consequently, HIV infection. The creation of "friendly" health centers like the one already in this city contributes to providing a comprehensive response to the problems faced by these women and encourages use of the health system. It therefore helps reverse their vulnerability and higher risk of contracting HIV and other sexually transmitted infections.