HIV-related stigma among people living with HIV (PLHIV) is associated with worse health outcomes. We used longitudinal data from a multisite cohort in South Africa to assess changes over time in stigma after HIV diagnosis and determine whether antiretroviral therapy (ART) initiation is associated with stigma reduction. We administered the Internalized AIDS-Related Stigma Scale (IARSS, a six-item dichotomous scale questionnaire) at baseline, 3 months, and 6 months to newly diagnosed ART-eligible participants between 2014 and 2015. A confirmatory factor analysis indicated that the IARSS contained a four-item internalized stigma factor (α = .80) and a two-item disclosure concerns factor (α = .75). We fitted multiple logistic regression models specifying internalized stigma/disclosure concerns at 6 months as the outcome and ART initiation as the predictor of interest. Of the 500 participants (187 men and 313 women) enrolled, 308 (62%) initiated ART. Internalized stigma declined among people entering care (mean score, 1.0 to 0.7, p < .01); however, disclosure concerns remained unchanged (percentage endorsing either disclosure concern item, 78% to 77%, p = .23). These findings were similar between ART initiators and noninitiators. We estimated a statistically significant positive association between ART initiation and disclosure concerns at 6 months (odds ratio [OR] = 1.88; 95% CI [1.20, 2.94]) but not between ART initiation and internalized stigma at 6 months (OR = 1.15; 95% CI [0.75, 1.78]). Among ART-eligible South African PLHIV entering into HIV care, internalized stigma modestly declined over time but disclosure concerns persisted. PLHIV who initiated ART were more likely to have persistent disclosure concerns over time as compared with those who did not start ART. (PsycINFO Database Record (c) 2019 APA, all rights reserved)