From 2018 to 2024, the Russian Federation witnessed an increase in the number of young people with perinatally acquired HIV (PHIV) who reached the age of 18 years and transitioned to adult care. It is known that young individuals with PHIV have a duration of HIV infection equal to their age (more than 18 years), with delayed or late initiation of antiretroviral therapy (ART), often in the setting of advanced disease stages. In addition to the direct damaging effect of HIV and the associated chronic inflammation, the toxic effects of certain antiretroviral drugs (ARVs) are well documented; their use has been accompanied by a significant number of adverse events and side effects, which have led to the need for ART regimen changes.The aim. To analyze the dynamics of HIV infection treatment in young people with perinatally acquired HIV infection from the time of ART initiation up to the present.Materials and methods. A retrospective-prospective study using consecutive sampling included 105 adult patients with PHIV, born between 1999 and 2005, who had been under dispensary follow-up at the St. Petersburg AIDS Center (AC) since childhood. An analysis of epidemiological, clinical, and laboratory parameters was performed for the period from birth to 2025 inclusive. Retrospectively, the following were assessed: age at HIV diagnosis and at treatment initiation, ART regimens, frequency of adverse events (AEs) and side effects (SEs) of ARVs, and reasons for switching therapy regimens. Prospectively (2019–2025), ART regimens, virological, immunological, and clinical efficacy of ART after patients’ transition to adult care, as well as treatment adherence, were analyzed. Statistical analysis of the obtained clinical data was performed using STATISTICA for Windows (version 12).Results and discussion. At the time of HIV diagnosis, the mean age of children was 2.6±4.3 years (min — first days of life, max — 17.4 years); the age at ART initiation was 7.2±4.5 years; the median interval between diagnosis and treatment start was 4.6 years. At treatment initiation, two-thirds of patients had immunodeficiency of varying severity. Initial ART regimens included protease inhibitors (PIs) in 95.2% of cases; they were highly effective, but required substitution in 78% of patients, mainly due to adverse events (54.3%), among which hematologic disorders, dyslipidemia, and peripheral neuropathy predominated. By the time of transition to adult care, 85.7% of patients were receiving ART as fixed-dose combinations (FDCs). Nevertheless, 16.2% of patients (n=17) discontinued treatment. Among those remaining under follow-up (n=88), 25.6% (n=21) had immunodeficiency three years after transition, and 13 (15.8%) individuals had detectable viral load.Conclusion. Thus, the cohort of adult patients with PHIV is characterized by a long disease duration, late initiation of antiretroviral therapy, a high incidence of adverse events and side effects associated with highly toxic antiretroviral drugs, and multiple treatment regimen switches. Fatigue resulting from lifelong medication intake was accompanied by reduced treatment adherence after transition to the adult AIDS Center department, leading to the loss of a significant proportion of patients from follow-up. Optimization of ART by switching children to new drugs in the form of fixed-dose combinations with a low toxicity profile was the main reason for regimen changes starting from the third line of therapy, and contributed to retaining the majority of adolescents — and subsequently adult PHIV patients — on treatment. As a result of high treatment adherence among patients who remained under the care of AC specialists, no clinical manifestations of HIV disease progression were observed.