ABSTRACT Objective: Assess the level of health literacy of adults, with and without hypertension, treated in three basic health units (UBS) in Picos, Piauí. Methods: Cross-sectional study conducted with 357 adults. Data were collected using a questionnaire with sociodemographic variables, and literacy was assessed by the Test of Functional Literacy in Adults. Descriptive analysis was performed followed by the association between literacy and exposure variables with Pearson’s chi-squared (X2) test and Mann-Whitney U test. Results: Inadequate or marginal health literacy was found in three units investigated (71.5%; 77.8% and 85.2%);. Age and the years of schooling were factors associated with inadequate literacy in adults with hypertension (p<0.0001). Conclusion: Inadequate literacy was found in more than 70% of the hypertensive patients investigated. This finding reinforces the need to improve the self-care skills of hypertensive patients, especially the older ones and those with few years of schooling.