Migrants from sub-Saharan Africa bear a disproportionate burden of HIV infection in Europe, with an increasing proportion of them acquiring HIV after migration. This transformation in the epidemic pattern has raised concerns about the sexual mixing and preventive behaviours of migrants. This paper aims at exploring how racial boundaries shape sexual networks and structure prevention practices among migrants from sub-Saharan Africa. Analyses are based on a French survey carried out among 1874 individuals born in sub-Saharan Africa, aged 18-49 and living in Paris and its surroundings. Our results provide evidence of the existence of African sexual networks, over and beyond those of national origin. The intra-African segregation of these sexual networks leads to sexual contacts between migrants from low- and high-HIV prevalence countries, which probably contribute to the development of the epidemic amongst these migrants. Moreover, racially-based perceptions of HIV-related risk seem to produce a specific attitude toward prevention practices as shown by higher rates of condom use among migrant women from sub-Saharan Africa with a partner born outside sub-Saharan Africa. As a consequence, community-based approaches to HIV prevention should take into account the identification of migrants from sub-Saharan Africa as a racial minority and not only focus on national borders.