The aim of this cross-sectional study was to analyze differences between Roma and non-Roma sex workers (SWs) according to their HIV/AIDS risk behaviors. In this study 91 Roma and 100 non-Roma SWs were included. They offered sex services at Belgrade hot spots during the period 2006-2007. Roma SW were significantly younger and with lower education and they were significantly more often without reading and writing skills than non Roma SW. They also significantly more often had the first sexual intercourse before an age of 14 years. Roma and non-Roma SWs did not differ significantly in their risky sex behaviors. Out of all SWs (both Roma and non-Roma) 13.6% had more than 5 clients daily, 61.3% always used a condom with the commercial sex partners and 17.3% always used a condom with the steady partner. More than half of all participants (55.0%) reported daily use of some psychoactive substance. Correct answers to all 6 standardized questions regarding HIV transmission gave only 9.9% Roma and 5.0% non-Roma SW and mean scores were 2.87 for Roma and 3.03 for non-Roma SW. These differences were not significant. According to multivariate analysis, Roma SWs were significantly younger, less educated, and with more testing to HIV during life in comparison with non Roma SWs. Significantly protective determinants for Roma SWs were knowledge of reading and writing and less frequently daily using of ecstasy during last month in comparison with non Roma SWs. It is necessary to continue work on education of both Roma and non-Roma SWs and to reconsider and revise the existing prevention programs regarding their impact on HIV transmission knowledge and the respective protective behaviors.