This paper describes use of the prescription records of a large pharmaceutical benefits management organization to retrospectively analyze the refill behavior of patients who have recently started antihypertensive therapy in the outpatient setting. Using logistic regression analysis, the author identified class of antihypertensive medication, patient age, and dosing frequency as clinically important independent covariates that are predictive of persistence (defined as continuing therapy with the original antihypertensive drug as originally prescribed) at 12 months. At 12 months' follow-up, the percentage of patients continuing initial angiotensin II (A-II) antagonist therapy was substantially higher than the percentage continuing therapy with angiotensin-converting enzyme inhibitors, calcium antagonists, beta-blockers, or thiazide diuretics (64% vs 58%, 50%, 43%, and 38%, respectively). Additional studies are needed to explain why more patients continued with the same A-II antagonist therapy at 12 months compared with the other classes of antihypertensive drugs; whether these findings are explained by drug tolerability, financial incentives, newness of the product, selection bias, or other factors; whether these differences will be maintained in the following years; and whether the differences are associated with better health outcomes.