Introduction. 44 cases of HIV-infection among the homeless were registered in Saint Petersburg in 2021. At the same time, it is known that the case reporting and medical treatment in Russia are limited by the lack of required document minimum among a large number of them — passport and compulsory medical insurance policy. The cohort of the homeless is heterogeneous and in many countries the predominant risk factors of HIV infection and prevalence are different. So far, the studies of HIV spread among the homeless in Russia are rare.Objective. Assess the prevalence of HIV infection among the homeless in Saint Petersburg.Materials and methods. Cross-sectional study was carried out among the homeless in «places of attraction»: heating points, overnight shelters, care services from May, 24th to October, 1st 2021 and involved 199 participants. There was questionnaire and rapid HIV antibody testing in capillary blood by the set «Wondfo HIV 1,2». The study was completed anonymously.Results. When examining HIV infection was detected in 9 out of 199 participants — 4.5% (CI 95% [1.61%, 7.39%]), thus, HIV prevalence among the homeless is on average higher than in Saint Petersburg (0.81%) and the country (0.78%). The factors, associated with HIV infection, are the use of injection drugs: odds ratio of prevalence in the adjusted model adjusted prevalence ratio (APR)=4.3 (p<0.05, CI 95% [1.1, 17.5]) and incarceration: APR=9.4 (CI 95% [1.1, 82.2]).Conclusion. The results obtained and the factors, defined in the study of risk factors for infection, allow to determine the main directions of HIV prevention among the homeless and to highlight the need for attributing the cohort of the homeless to the «key» population group along with others.