This study examines the psychometric properties and tests the concurrent and predictive validity of a structured, self-reported medication adherence measure in patients with hypertension. The authors also assessed various psychosocial determinants of adherence, such as knowledge, social support, satisfaction with care, and complexity of the medical regimen. A total of 1367 patients participated in the study; mean age was 52.5 years, 40.8% were male, 76.5% were black, 50.8% graduated from high school, 26% were married, and 54.1% had income <$5,000. The 8-item medication adherence scale was reliable (α=.83) and significantly associated with blood pressure control (P<.05). Using a cutpoint of <6, the sensitivity of the measure to identify patients with poor blood pressure control was estimated to be 93%, and the specificity was 53%. The medication adherence measure proved to be reliable, with good concurrent and predictive validity in primarily low-income, minority patients with hypertension and might function as a screening tool in outpatient settings with other patient groups.