Objective. To evidence the relationship between the degree of health literacy and adherence to the treatment of chronic diseases in a primary care center. Methods. Cross-sectional-analytic-observational study; 326 patients with a diagnosis of arterial hypertension or diabetes mellitus were taken between December 1, 2020 and March 27, 2021. Questionnaires were applied to measure the level of health literacy, as well as adherence to pharmacological and nonpharmacological treatment. The results were statistically compared with the Chi-square test to evaluate the association between the degree of health literacy and adherence to treatment in patients with arterial hypertension (AHT) and diabetes mellitus (DM). Results. 51.84 % had only AHT, 19.02 % had DM and 29.14 % had both AHT and DM. 69.3 % had sufcient health literacy, while 30.7 % had inadequate health literacy. 25.2 % of patients are ...