OBJECTIVES: Although the importance of hypertension as a risk factor for cardiovascular disease (CVD) is well know, blood pressure remains uncontrolled in a significant part of patients. The aim of this study was to assess the cost-effectiveness of adding olmesartan, a angiotensin-II-antagonist, to treatment in patients with uncontrolled hypertension. Belgium was used as a case country. METHODS: A Markov model with a 10-year time horizon using 6-month cycles was developed in MSExcel. Depending on age, smoking status, systolic blood pressure (SBP), and total cholesterol, fatal CVD risk (cardiac death, fatal stroke) was calculated using the SCORE equation for patients without a history of CVD and using the Framingham equation for patients with a history of CVD (18%). Non-fatal risk was indirectly calculated based on landmark primary prevention trials. Clinical data were obtained from the Belgian 12-week Olme-R3-study (Olmetec Real-life Responder Rate-study) in which 4130 patients with uncontrolled hypertension were started on olmestartan (10, 20 or 40mg at the physician's discretion-74% received 20mg) assuming that effects are maintained over 10-years. Direct costs from the Belgian payers' perspective were included. Official sources for cost of events and cost of drugs were used. The unit costs of olmesartan, 10, 20 and 40mg are respectively €0.70, €0.50 and €0.63 (10mg more expensive due to pack-size). Annual discounting of 3% was applied on cost and effects. RESULTS: At 12 weeks, adding olmesartan decreased SBP with 22.47mmHg (95%CI 22.00-22.94mmHg - baseline SBP 160mmHg) and decreased the number of antihypertensive drugs needed. The cost of antihypertensive treatment increased from €0.54 to €0.73 (part olmesartan €0.53) per day. Applying the observed SBP effect to the 10-year model results in a incremental cost-effectiveness ratio of €9,813/LYG (95%CI €9,568/LYG-€10,073/LYG). CONCLUSIONS: Adding olmesartan to antihypertensive treatment in patients with uncontrolled hypertension seems cost-effective from the perspective of the health care payer.