Health literacy influences HIV treatment for youth and, thus, is a research priority. We explored health knowledge and self-reported adherence, as indicators of health literacy, among youth living with HIV (YLWH) and the association between health literacy and health outcomes. A total of 102 YLWH ages 13–25 years participated in the study. Participants completed the Brief Estimate of Health Knowledge and Action-HIV Version; CD4+ T-cell counts and viral loads were extracted from participant medical records. Participants had a moderate amount of HIV knowledge, and most reported taking their medications under most conditions. Decreasing action scores were statistically associated with an increased likelihood of having a detectable viral load. Health literacy is an important factor that should be addressed by practitioners working with YLWH. More research is needed to determine the best way to measure and improve health literacy.