Rates of HIV-1 infection are growing rapidly, and the epidemic of sexually transmitted infections is continuing at an alarming rate, in the Russian Federation. We did a cross-sectional study of sexually transmitted infections, HIV infection, and drug use in street youth at a juvenile detention facility, adults at homeless detention centres, and women and men at a remand centre in Moscow. 160 (79%) women at the remand centre were sex workers. 91 (51%) homeless women had syphilis. At least one bacterial sexually transmitted infection was present in 97 (58%) female juvenile detainees, 120 (64%) women at the remand centre, and 133 (75%) homeless women. HIV seroprevalence was high in women at the remand centre (n=7 [4%]), adolescent male detainees (5 [3%]), and homeless women (4 [2%]). In view of the interaction between sexually transmitted infections and HIV infection, these findings of high prevalence of sexually transmitted infections show that these disenfranchised populations have the potential to make a disproportionately high contribution to the explosive growth of the HIV epidemic unless interventions targeting these groups are implemented in the Russian Federation.