HIV-related stigma among persons living with HIV/AIDS (PLHIV) is prevalent throughout sub-Saharan Africa. There is limited evidence, however, on which interventions are effective in reducing it. We used data from a prospective impact evaluation of a 12-month food assistance intervention among 904 antiretroviral therapy (ART)- naïve PLHIV in Uganda to examine the program impact on stigma. Stigma was measured using the comprehensive HASI-P scale, which demonstrated good internal consistency (Cronbach's alpha = 0.87) and was correlated with several related constructs including physical and mental health-related quality of life, disclosure, and physical health symptoms in the sample. Using quasi-experimental difference-in-difference matching methods to better infer causality, we tested whether the intervention improved the overall stigma scale and its subscales. The food assistance intervention had a significant effect on reported internalized (but not external) stigma of approximately 0.2 SD (p < 0.01). The HASI-P stigma scale is a useful tool for measuring and tracking stigma. Food assistance interventions, embedded in an HIV care program, can reduce internalized stigma.