Background: Low adherence to antihypertensive medication is an important barrier to achieving blood pressure control. Few data are available for medication adherence in adults with chronic kidney disease (CKD). Study Design: Cross-sectional. Setting & Participants: 3,936 and 9,129 participants with and without CKD using antihypertensive medication in the REGARDS (Reasons for Geographic and Racial Differences in Stroke) Study, respectively. CKD was defined as albuminuria with albumin excretion ≥30 mg/g or estimated glomerular filtration rate <60 mL/min/1.73 m2. Outcomes: Medication adherence and uncontrolled hypertension. Measurements: Medication adherence was assessed using a validated 4-item scale. Blood pressure was measured 2 times by trained staff. Results: In REGARDS participants with and without CKD, 1,426 (36.2%) and 2,421 (26.5%) had uncontrolled hypertension with blood pressure ≥140/90 mm Hg, and 2,656 (67.5%) and 5,627 (61.6%), ≥130/80 mm Hg. Also, 27.7% of those with CKD and 27.9% of those without CKD responded "yes" to ever forgetting to take their medication and 4.4% and 4.2%, respectively, responded yes to being careless about taking their medication. Also, 5.7% and 5.3% responded yes to missing taking medication when they felt better, and 4.2% and 3.6%, to missing it when they felt sick. Overall, 23.3% and 23.7% of participants with and without CKD responded yes to 1 adherence question, whereas 7.7% and 7.2%, respectively, responded yes to 2 or more adherence questions. In those with CKD, the multivariable adjusted ORs for uncontrolled hypertension (blood pressure ≥140/90 mm Hg) for individuals answering yes to 1 and 2 or more versus 0 adherence questions were 1.26 (95% CI, 1.05-1.51) and 1.49 (95% CI, 1.12-1.98), respectively. Analogous ORs for systolic/diastolic blood pressure ≥130/80 mm Hg were 1.06 (95% CI, 0.78-1.45) and 1.20 (95% CI, 0.88-1.64). Limitations: Pharmacy fill data were not available. Conclusions: Individuals with CKD had similarly poor medication-taking behaviors as those without CKD. © 2010 National Kidney Foundation, Inc.