The aim of this study was to determine the coreceptor tropism by performing genotypic HIV-1 tropism testing in a cohort of patients perinatally infected with HIV-1 and exposed to antiretroviral therapy. Genotypic coreceptor tropism was determined in patients with HIV-1 RNA100 copies/mL using plasma samples (set at a FPR of 20%), according to European guidelines. Out of 55 patients, 50 had an HIV-1 subtype B strain, and mean (SD) age was 18.2 (4.6) years. The median duration of antiretroviral therapy was 13 years (range, 3–23). Thirty-three (60%) patients harbored the R5 virus. At the time of the testing, the median CD4+ T lymphocyte cell count and percentage were 705 cells/mm3 (474–905) and 32.5% in group R5 and 626 cells/mm3 (450–755 …