Suboptimal control of hypertension in large communities can be attributed, in part, to about 50% of patients who stop taking their antihypertensive drugs after 1 year. Older patients with many illnesses (including chronic kidney disease) are at especially high risk for discontinuing prescribed medications, but age is a weaker predictor than the number of consumed pills. Determining if medications are being taken as prescribed is difficult, but asking the patient and significant other the simple question, "Have you missed any pills in the last week?" is a good place to start. Despite all their other virtues, clinical trials seldom provide the same answers regarding medication adherence that are found in clinical practice. Observational and a few interventional trials have established that short, simple regimens that improve patients' symptoms and are well tolerated are more likely to be taken correctly. Patient (and family) education is the cornerstone of improving adherence to medication, but several other interventions have also proven useful. There appears to be no "magic bullet" that will improve medication adherence in all patients, but providing written instructions, simplifying the medication regimen to as few as necessary, once daily, well tolerated and inexpensive pills, involving family members, and prompting pill taking by certain activities of daily living all seem to help. Improving medication adherence would be a simple way to make antihypertensive therapies much more cost effective, since a medication that is not taken incurs all of cost, and provides no benefit to the patient.