Patients with severe hypertension are at high risk for cardiovascular events. The authors hypothesized that initial treatment with a combination angiotensin receptor blocker/diuretic agent would be safe and more effective than initial treatment with a single agent for these patients. In this 6-week, double-blind trial, 585 patients were randomized to losartan/hydrochlorothiazide or losartan as monotherapy and titrated as needed at 2-week intervals to reach goal blood pressure (<90 mm Hg). Almost twice as many patients achieved goal at the primary end point of 4 weeks on 50 mg losartan/12.5 mg hydrochlorothiazide vs. the losartan regimen (50-100 mg; p=0.002). Additionally, almost three times as many patients achieved goal blood pressures at 6 weeks (p<0.001). Adverse experiences on losartan/hydrochlorothiazide (43%) were significantly less than with the angiotensin receptor blocker alone (52.6%). This study confirmed the efficacy and tolerability of initial use of a fixed combination of losartan/hydrochlorothiazide vs. losartan without a thiazide.