BackgroundSelf-reported antiretroviral therapy (ART) adherence measures that are associated with plasma viral load (VL) are valuable to clinicians and researchers, but are rarely examined among groups vulnerable to dropping out of care. One-seventh of all those living with HIV pass through incarceration annually and criminal-justice (CJ) involved people living with HIV (PLH) are vulnerable to falling out of care. We examined the association of self-reported ART adherence with VL in a criminal-justice sample compared to a routine-care sample.MethodsSamples: We examined data from a multisite collaboration of studies addressing the continuum of HIV care among CjJ involved persons in the Seek, Test, Treat, and Retain cohort. Data pooled from seven CJ- studies (n = 414) were examined and compared with the routine-care sample from the Centers for AIDS Research Network of Integrated Clinical Systems’ seven sites (n = 11,698).Measures: In both samples, data on self-reported percent ART doses taken were collected via the visual analogue scale adherence measure. Viral load data were obtained by blood-draw.Analysis: We examined the associations of adherence with VL in both cohorts using mixed effects linear regression of log-VL, and mixed effects logistic regression of binary VL (≥ 200 copies/mL) outcomes. Interactions by CD4 count and self-reported health status were also tested.ResultsAmong the CJ sample, the coefficient for log-VL was − 0.31 (95% CI = − 0.43, − 0.18; P < 0.01) and that in the routine-care sample was − 0.42 (95% CI = − 0.45, − 0.38; P < 0.01). For the logistic regression of binary detectable VL on 10% increments of adherence we found the coefficient was − 0.26 (95% CI = − 0.37, − 0.14; P < 0.01) and in the routine-care sample it was − 0.38 (95% CI = − 0.41, − 0.35; P < 0.01). There was no significant interaction by CD4 count level in the CJ sample, but there was in the routine-care sample. Conversely, there was a significant interaction by self-reported health status level in the criminal-justice sample, but not in the routine-care sample.ConclusionsThe visual analogue scale is valid and useful to measure ART adherence, supporting treatment for CJ- involved PLH vulnerable to falling out of care. Research should examine adherence and VL in additional populations.