Almeida et al. report, in this issue of the journal, a retrospective studyon theprevalence and patterns of antiretroviral drug resistance in 24 treatment-naive and 23 treatment-experienced children failing therapy between 2000 and 2004 attending a clinic in Sao Paulo. All children were vertically infected, and the median age of the naiveand treatment-experienced children was 22 months and 102 months, respectively. In the children failing ART, the median duration of ART exposure was 60 months (range3-120months), and the log viral load at treatment failure was 5.04 log copies/mL. The overall distribution of subtypes among both groups of children was 78.3% subtype B, 13% subtype F, 4.4%BFmosaics and 4.3% subtype C, which reflects thedistinctivemolecular epidemiologyofHIV-1 inBrazil, with the low-level but rising prevalence of subtypeC infection in the south of the country.