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The human immunodeficiency virus type 1 (HIV-1) can be transmitted via parenteral, sexual, or vertical exposure routes. The number of HIV-1 cases detected yearly in children and adolescents in Brazil did not decrease over the last decade, representing ~5% of total cases described in the country. In recent years, the HIV-1 diversity and the prevalence of transmitted drug resistance mutations (TDRM) are moving toward a marked increase. In this study, we retrospectively evaluated the diversity of HIV-1 subtypes and the TDRM prevalence in 135 treatment-naïve HIV-1 vertically infected children and adolescents born in between 1993 and 2012. These children were assessed in either 2001-2007 or 2008-2012 when they were 0 to 17 years old. The individuals assessed in 2001-2007 ( n = 38) had median CD4+ T cell counts of 1218 cells/mm 3 (IQR: 738-2.084) and median HIV-1 plasma viral load of 4.18 log10 copies/mL (IQR: 3.88-4.08). The individuals ( n = 97) evaluated in 2008-2012 showed median CD4+ T cell counts of 898.5 cells/mm 3 (IQR: 591.3-1.821) and median HIV-1 plasma viral load of 4.69 log10 copies/mL (IQR: 4.26-5.33). A steady decrease in the median CD4 T+ cell counts was observed with age progression, as expected. The majority HIV-1 pol sequences (87%) were classified as pure HIV-1 subtypes (77% subtype B, 9% subtype F1 and 1.5% subtype C), while 13% of sequences were classified as recombinants (CRF45_cpx, n = 4; CRF28/29_BF1, n = 2; CRF02_AG, n = 1; CRF40_BF1, n = 1, CRF99_BF1, n = 1, URF_BF1, n = 8). The overall prevalence of TDRM was 14% (19/135), conferring resistance to the nucleoside reverse transcriptase inhibitors (NRTI, 13/135-9.6%), non-nucleoside reverse transcriptase inhibitors (NNRTI, 8/135-5.9%), and protease inhibitors (PI, 2/135-1.5%). The main TDRM observed for NNRTI was the K103N ( n = 8), while the mutations T215I/Y/D/E ( n = 7) and M184V ( n = 4) were the main TDRM for NRTI. Only two TDRM were observed for PI in one individual each (M46I and V82A). Most TDRM were found in the HIV-1 subtype B (84%) sequences. This study reveals an HIV-1 epidemic with high diversity and moderate prevalence of TDRM in the pediatric population of Rio de Janeiro, indicating the existence of possible problems in the clinical management of prophylactic therapy to prevent mother-to-child transmission and future treatment options for the affected children.