OBJECTIVES The purpose of this study was to test the theoretical model of whether patient's efficacy expectations and outcome expectations mediate the relationship between health literacy and medication adherence. In addition, the relationships between patients' demographic variables and their health literacy skills, outcome expectations, efficacy expectations and medication adherence were evaluated METHODS A survey composed of four validated instruments along with questions related to patient's demographic information was utilized. The four validated instruments assessed functional health literacy (S-TOFHLA), medication related outcome expectations and efficacy expectations and medication adherence (MARS). The questionnaire was pretested by conducting a pilot study of 21 patients with hypertension at a community health clinic. RESULTS In the main study 200 patients with hypertension completed the self-administered survey. Path analysis was used to test the theoretical model. Age had statistically significant associations with health literacy scores (ñ = -0.17, p =0.015), efficacy expectations (ñ =0.23, p =0.004), and medication adherence (ñ =0.27, p = <0.0001). In addition, number of prescriptions taken daily and insurance (t = -5.30, p = <0.001) had a statistically significant association with medication adherence (ñ =0.16, p = 0.024). Health literacy was only variable that was statistically correlated with income (ñ = 0.21, p =0.003) and level of education (ñ = 0.29, p =0.001). Path analysis indicated that medication adherence was significantly associated with age and efficacy expectations, which also was related to health literacy level, age and income. Health literacy was also a significant predictor of outcome expectations. Gender, level of education, and income were the only demographic variables significantly associated with health literacy scores. CONCLUSIONS The results of the study suggested that health literacy had an impact on medication adherence through efficacy expectations.