© 2017 American Society of Hypertension The purpose of this study was to test the association between a self-report measure of 24-hour adherence to antihypertensive medication and blood pressure (BP) among African Americans. The primary analysis included 3558 Jackson Heart Study participants taking antihypertensive medication who had adherence data for at least one study examination. Nonadherence was defined by self-report of not taking one or more prescribed antihypertensive medications, identified during pill bottle review, in the past 24 hours. Nonadherence and clinic BP were assessed at Exam 1 (2000–2004), Exam 2 (2005–2008), and Exam 3 (2009–2013). Associations of nonadherence with clinic BP and uncontrolled BP (systolic BP ≥ 140 mm Hg or diastolic BP ≥ 90 mm Hg) were evaluated using unadjusted and adjusted linear and Poisson repeated measures regression models. The prevalence of nonadherence to antihypertensive medications was 25.4% at Exam 1, 28.7% at Exam 2, and 28.5% at Exam 3. Nonadherence was associated with higher systolic BP (3.38 mm Hg) and diastolic BP (1.47 mm Hg) in fully adjusted repeated measures analysis. Nonadherence was also associated with uncontrolled BP (prevalence ratio = 1.26; 95% confidence interval = 1.16–1.37). This new self-report measure may be useful for identifying nonadherence to antihypertensive medication in future epidemiologic studies.