Purpose: The purposes of this study were to identify the level of health literacy and to determine its impact on disease-related knowledge and adherence to self-care in adults with hypertension. Methods: This was a cross-sectional, descriptive study in which patients with hypertension were recruited from outpatient hypertension clinics in Seoul, Korea from December, 2009 to February, 2010. A total 186 patients completed series of questionnaires to assess health literacy, disease-related knowledge, and adherence to self-care. Hierarchical linear regression was used to determine whether health literacy was associated with disease-related knowledge and adherence to self-care. Results: Seventy-one (38.2%) and seventy-two (38.7%) patients had inadequate and marginal health literacy, respectively. In hierarchical linear regression, health literacy independently predicted disease-related knowledge (${eta}$= .43, p < .001) and adherence to self-care (${eta}$= .37, p < .001) after controlling for age, education level, having a job or not, and body mass index. Conclusion: These findings show that health care providers need to pay attention to patients with hypertension who have inadequate health literacy. Further, it is recommended to develop and implement new strategies for assessing health literacy in clinical practices. Interventions to improve health literacy could promote disease-related knowledge and adherence to self-care in patients with hypertension.