The aim of the study is to study the main pathways and risk factors for HIV infection in a child, to establish a probable source of infection for a child, as well as to exclude the possibility of criminal or nosocomial infection.Materials and methods. At the first stage, an epidemiological investigation was conducted. Next, a molecular genetic analysis of two blood plasma samples studied (child and mother) and a comparison group were used, in which 18 nucleotide sequences of HIV-1 variants were used, obtained from patients living in the Primorsky Region, and 8 characterized nucleotide sequences additionally taken from GenBank international database. Distance calculation and phylogenetic analysis were performed by constructing phylogenetic trees using the Maximum Likelihood method using the GTR evolution model.Research results. The data obtained indicate that the nucleotide sequence from the child is most similar to the nucleotide sequence from the mother (potential source) and reliably grouped on the phylogenetic tree, forming a common cluster that is different from the samples of the comparison group. This indicates the likelihood of an epidemiological link between HIV infections in the mother and her child.Conclusion. According to the results of this study, we can conclude that the child is infected from an HIV-infected mother, approximately at the age of a child older than 4 years old, when he received the last negative test result for HIV markers.