OBJECTIVES: The Joint National Committee for the Prevention, Detection and Treatment of High Blood Pressure (JNC-VI) has published guidelines recommending thiazide diuretics (TZDs) or beta-blockers for the initial medication management of hypertension. Recent studies have corroborated these guidelines by demonstrating no difference in morbidity and mortality between chlorthalidone, amlodapine, and lisinopril in the treatment of hypertension. Thus, selection between these agents represents an issue of cost with similar outcomes. Hamilton and Clause have reported the prevalence of these agents for the treatment of hypertension in a sample of NYS Medicaid recipients, and observed variances from treatment guidelines. Using their results and the NYS Medicaid prescription database, differences in costs for single-agent treatments were assessed. METHODS: Prescription utilization data were abstracted from the NYS Medicaid claims database for a sample of 2689 beneficiaries with hypertension in 1999. Three groups were identified: a) 267 receiving only a TZD; b) 964 receiving only a calcium antagonist (CA); and c) 941 receiving either an ACEI or an ARB. Medicaid costs and days supply were queried for the following drug classes: a) ACEI; b) ARB; c) CA; and d) TZDs. Average cost-per-day were calculated for each category. Results were then adjusted for previously observed variances from treatment guidelines. RESULTS: Cost/day for each group were as follows: a) $0.18/day for TZDs; b) $1.58/day for CA; and c) $1.18/day for ACEI or ARBs. Compared to TZD, the excess costs for inappropriate CA therapy were estimated at $1.40/day or $511 per patient per year. Total potential patients benefiting from appropriate therapy were estimated from national trends. With 328,578 hypertensive NYS Medicaid patients, inappropriate therapies could account for more than $ 4.2 million in excess expenditures. CONCLUSION: There is potential for significant annual savings to NYS Medicaid through improved application of JNC-VI guidelines to the initial treatment of hypertension.