['Inversion of the CD4:CD8 ratio is a marker of immune activation and age-associated disease. We measured the CD4:CD8 ratio as a marker of cognitive impairment in HIV-infected patients and explored differences according to clinical severity.', 'Post hoc analysis of data from two prospective cohorts of HIV-infected patients randomly selected to undergo neuropsychological tests was performed. Test scores were adjusted for age, gender and education. Inclusion criteria were undetectable viral load and stable treatment for at least 6 months. Subjects with HIV-associated dementia were excluded. Patients were divided into an unimpaired group, a group with asymptomatic neurocognitive disorder (ANI) and a group with symptomatic HIV-associated neurocognitive disorder (sHAND), represented by mild neurocognitive disorder (MND). Demographic and background parameters, immune activation markers and the CD4:CD8 ratio were recorded.', 'Two hundred patients were included in the study. The mean age was 52 years, 78% were male, the mean CD4 count was 624\u2009cells/μL, the mean nadir CD4 count was 240\u2009cells/μL, 27% were hepatitis C virus (HCV)-coinfected, the mean duration of HIV infection was 16 years, and the mean time on current combination antiretroviral therapy (cART) was 2.9 years. Twenty-nine per cent of subjects had HAND (21% had ANI and 8% had MND). In multivariate analysis, a CD4:CD8 ratio\u2009<\u20091 was associated with a nadir CD4 count\u2009<\u2009200\u2009cells/μL [odds ratio (OR) 3.68] and with the presence of CD4(+) CD38(+) HLA(+) cells (OR 1.23). Multinominal logistic regression showed that, in comparison with the unimpaired group, diagnosis of sHAND was associated with a CD4:CD8 ratio\u2009<\u20091 (OR 10.62), longer HIV infection (OR 1.15) and longer current cART (OR 1.34), while the ANI group differed from the unimpaired group only for education level.'] Do virologically suppressed patients with asymptomatic and symptomatic HIV-associated neurocognitive disorders display the same pattern of immune activation?