This research explores the association between the interruption or termination of antihypertensive drug therapy and total health care costs among non-institutionalized Medicaid patients older than age 40 who survive the first year after treatment. Multivariate regression analysis was used to estimate the statistical relationship between post-treatment costs and patient demographic characteristics, prior use of services, the type of medication used as initial therapy and whether the patient maintained continuous therapy. Paid claims data from the California Medicaid (Medi-Cal) program were used in the analysis. Total cost of health care in the first year after the initiation of drug therapy was the primary outcome variable. Components of total costs (e.g., hospital, outpatient and physician services, prescription drugs) were also investigated. Nearly 86% of new antihypertensive drug therapy patients interrupted or discontinued purchasing any form of antihypertensive medication during the first year. Patients with interrupted antihypertensive drug therapy consumed an additional $873 per patient (P < .0001) in health care during the first year, not counting a reduction in prescription drug cost of $281 (P < .0001). Increased costs were primarily due to increased hospital expenditures of $637 (P < .0002).