Objective: To study socio-demographics, sexual practices, drug use behaviors, and prevalences of HIV, syphilis, hepatitis B and C, HTLV-1 and HTLV-2 in immigrant (foreigner) and non-immigrant (local/native) female sex workers (FSW). Design: This was a cross-sectional study in immigrant and non-immigrant FSW living in Buenos Aires, Argentina. Participants were interviewed using a standardized questionnaire. Results: A total of 625 FSW were enrolled, of whom 169 (27%) were immigrant FSW from Paraguay, the Dominican Republic, Brazil, Peru, and Uruguay. The prevalence of syphilis and hepatitis C was significantly higher among Argentinean FSW than among immigrant FSW. However, hepatitis B prevalence was higher among immigrant FSW. Adjusted risk factor analysis comparing immigrant FSW with Argentinean FSW indicated that marital status (single), occupation (none), fee per sex act (≤US$7), workplace (bar and cabaret), and anal sex with clients were significantly associated with immigrant FSW status. Conclusions: Effective HIV/STI prevention and medical care programs need to be tailored to the specific needs of both FSW groups in Argentina. © Springer Science+Business Media, LLC 2008.