Low adherence to antihypertensive medication remains a public health challenge. Understanding barriers to, and determinants of, adherence to antihypertensive medication may help identify interventions to increase adherence and improve outcomes. The Cohort Study of Medication Adherence in Older Adults is designed to assess risk factors for low antihypertensive medication adherence, explore differences across age, gender, and race subgroups, and determine the relationship of adherence with blood pressure control and cardiovascular outcomes over time. This article discusses the relevance of this study in addressing the issue of barriers to anithypertensive medication adherence.