ABSTRACT Objective: To analyze the relationship between health literacy and medication adherence of patients with Type 2 Diabetes Mellitus. Method: Quantitative cross-sectional study developed in five Family Health Strategies in the city of Picos, Piauí. Participants comprised 78 users of health services. The “Short Test of Functional Health Literacy in Adults” and the “Treatment Adherence Measurement Test” forms were applied to obtain sociodemographic variables. Descriptive and inferential statistical analysis. Results: Regarding health literacy, 51.3% of the participants were considered inadequate, and 87.2% were adherent to the drug treatment. The average of health literacy varied according to the level of medication adherence and sociodemographic variables. Conclusion: Most patients reported to adhere to the medication. Implications for practice: This study identified the health literacy and medication adherence profile of the patients, thus subsidizing the planning of nursing interventions in the attention of diabetes mellitus.