To assess the efficacy of individually optimized doses of olmesartan medoxomil compared to losartan in elderly and very elderly patients with essential hypertension. The study hypothesis is non-inferiority of olmesartan medoxomil compared to losartan in lowering mean sitting diastolic blood pressure after 12 weeks of treatment compared to baseline. The study duration is up to 60 weeks, including a 52-week treatment period. After 12 weeks of treatment hydrochlorothiazide may be added to control blood pressure. Efficacy and safety measurements are carried out at up to 18 visits during the trial.