HIV-associated neurocognitive disorder (HAND) persists in the combination antiretroviral therapy (cART) era and is associated with diminished quality of life. The disorder remains challenging to diagnose given the requirement for comprehensive neuropsychological testing. Blood biomarkers are needed to facilitate the diagnosis of HAND and to gauge neurological response to antiretroviral therapy. We performed a study of plasma neurofilament light chain (NFL) that included 37 HIV-infected and 54 HIV-negative adults. In the univariate mixed-effect model involving HIV-infected participants, there was a statistically significant linear relationship between composite neuropsychological score (NPT-11) and plasma NFL (slope = − 9.9, standard error = 3.0 with 95% confidence interval − 3.2 to − 16.6 and p = 0.008 when testing slope = 0). Similarly, in the multivariate mixed-effect model, higher plasma NFL was significantly associated with worse NPT-11 (slope = − 11.5, standard error = 3.3 with 95% confidence interval − 3.7 to − 19.0 and p = 0.01 when testing slope = 0). The association between NPT-11 and NFL appeared to be driven by the group of individuals off cART. In a subset of participants who had visits before and after 24 weeks on cART (n = 11), plasma NFL declined over time (median = 22.7 versus 13.4 pg/ml, p = 0.02). In contrast, plasma NFL tended to increase over time among HIV-negative participants (median 10.3 versus 12.6 pg/ml, p = 0.065, n = 54). Plasma NFL therefore shows promise as a marker of neuropsychological performance during HIV. Larger studies are needed to determine if NFL could serve as a diagnostic tool for HAND during suppressive cART.