Self-efficacy, a known predictor of a wide range of health behaviors, has not been investigated in studies of adherence to antihypertensive medications. A medication adherence self-efficacy scale was developed and evaluated in ambulatory hypertensive African-American patients in two sequential phases. For the item-generation phase, open-ended interviews with 106 patients were used to elicit their experiences with taking antihypertensive medications. Using qualitative techniques, responses were recorded verbatim, coded, and sorted into nine categories of barriers and facilitators of medication adherence. Concepts from categories were formatted into an initial 43-item self-efficacy questionnaire, which was administered to another group of 72 patients for the item analyses phase. Twenty-six items were retained for the final self-efficacy scale based on item-to-total correlation coefficient >0.5, kappa >0.4, and clinical relevance of individual items. Clinicians and researchers can use this scale to identify situations in which patients have low self-efficacy in adhering to prescribed medications.