The objective of this study was to assess the frequency of blood-brain barrier (BBB) impairment, as measured by the albumin ratio, in neuro-asymptomatic HIV-1-infected individuals without antiretroviral treatment and the correlation between BBB disruption and intrathecal immune activation and HIV-1 RNA levels. Serum and cerebrospinal fluid (CSF) albumin, neopterin, and HIV-1 RNA levels were analysed in 110 neuro-asymptomatic HIV-1-infected individuals at different stages of disease; 63 classified as CDC A, 25 as CDC B, and 22 as CDC C. Increased BBB permeability was found in 17 of 110 (15%) of HIV-1-infected individuals. This proportion was sustained throughout the CDC stages. The albumin ratio was correlated with the CSF neopterin levels (r(s) = 0.36, P < 0.001), the serum neopterin levels (r(s) = 0.37, P < 0.001), and the CSF HIV-1 RNA levels (r(s) = 0.26, P < 0.01), but not with the plasma HIV-1 RNA levels. The correlations between the albumin ratio and the CSF and serum neopterin concentrations and the CSF HIV-1 RNA levels indicate that immune activation and, possibly, intrathecal HIV-1 virus replication are important factors associated with increased BBB permeability in HIV-1 infection.