The threat of social stigma may prevent people living with HIV from revealing their status to others and serve as a barrier to HIV treatment adherence. We evaluated the effect of such concerns on self-reported treatment adherence using a short, three-item measure among 204 people living with HIV. Overall, the mean age of participants was 40.1 years, 45% were African American, and 80% were male. People with high HIV stigma concerns were 2.5 times less likely to define and interpret the meaning of CD4 count correctly and 3.3 times more likely to be nonadherent to their medication regimen than those with low concerns. Concern over revealing HIV status was the only statistically significant, independent predictor of adherence in multivariate analysis. Clinical care directed to individuals living with HIV should therefore include considerations for patient sensitivity to social stigma, such as modifications to medication schedules and referrals for counseling prior to enrollment in antiretroviral therapies.