Antiretroviral therapy (ART) has improved survival into adulthood for young people with perinatally acquired HIV-1 (yp-PaHIV), but long-term prognosis remains unclear. We hypothesized that on-going immune activation, reflected in the failure of CD4:CD8 ratio normalization would be observed in yp-PaHIV, despite ART.A cross-sectional study of routinely collected clinical data from a cohort of yp-PaHIV (≥16 years).Data were collected from records of individuals attending a specialist clinic for yp-PaHIV transitioning to adult care. CD4:CD8 ratio and proportion with CD4:CD8 ratio ≥1, demographic data and viral parameters, including HIV-1 viral load (VL) and human cytomegalovirus (CMV) IgG, were analyzed with IBM SPSS Statistics v22.A total of 115 yp-PaHIV, median (IQR) age 22.0 (20.0-24.0) years, were studied, of whom 59 were females, and the majority were Black African 75/115 (65.2%). Where measured, CMV antibodies were frequently detected (71/74, 95.9%) and CMV IgG titre was inversely associated with CD4:CD8 ratio, (Rho -0.383, P = .012). Of those taking ART, 69 out of 90 (76.7%) yp-PaHIV had suppressed HIV viremia (<50 RNA copies/mL) and recovery of CD4:CD8 ratio to ≥1 was seen in 26 out of 69 (37.7%) with suppressed HIV viremia. Persistence of low CD4:CD8 ratio was observed even in those with a CD4 count ≥500 cells/μL, where 28/52 (53.8%) had a CD4:CD8 ratio <1. Of those with suppressed viremia, the median (IQR) age for starting ART was 8.0 (5.0-12.8) years and CD4:CD8 ratio was inversely associated with age at ART start, Rho -0.348, (P = .028).In this cohort of yp-PaHIV, despite lifelong HIV infection and widespread CMV coinfection, CD4:CD8 ratio recovery rate was comparable to adults treated in acute infection. Where persistence of CD4:CD8 ratio abnormality was observed, on-going immune activation may have significance for non-AIDS outcomes. Taken together our findings indicate immune resilience to be a feature of these adult survivors of perinatally acquired HIV infection, which can be supported with early antiretroviral therapy.