To compare the antihypertensive efficacy of the combination irbesartan/hydrochlorothiazide (HCTZ) using either a usual or an active elective titration regimen. The main efficacy criteria will be the change in mean Systolic Blood Pressure (SBP), measured at doctor's office with an automatic device, after a 10-week treatment period in hypertensive patients insufficiently controlled by monotherapy.

Inclusion Criteria:

• Established essential hypertension treated for at least 4 weeks by one antihypertensive drug alone
• With uncontrolled Blood Pressure (BP) defined as:
• SBP ≥ 160 mmHg and/or DBP ≥ 100 mmHg in non diabetic patients
• SBP ≥ 150 mmHg and/or DBP ≥ 90 mmHg in diabetic patients

Exclusion Criteria:

• SBP ≥ 180 mmHg and/or DBP ≥ 110 mmHg at V1
• Known or suspected causes of secondary hypertension
• Patient with bilateral renal artery stenosis, renal artery stenosis in a solitary kidney; history of renal transplant or only has one functioning kidney
• Associated cardiovascular conditions that prevent the patient from stopping the current antihypertensive drug (e.g.: Beta-blocker for angina, ACE-inhibitors for heart failure, etc…).
• Known hypersensitivity to diuretics or sulphonamides or history of angioedema or cough related to the administration of an angiotensin II receptor antagonist or any combination of the drugs used
• Known contraindications to the study drugs:
• Severe renal dysfunction (creatinine clearance <30ml/min)
• Known hypokaliemia (< 3 mmol/L) , known hypercalcemia
• Severe hepatic impairment, biliary cirrhosis, cholestasis
• Inability to obtain a valid automatic BP measurement recording
• Administration of any other investigational drug within 30 days prior to study entry and during the course of the study
• Presence of any severe medical or psychological condition that, in the opinion of the investigator, indicate that participation in the study is not in the best interest of the subject.
• Presence of any other conditions (e.g. geographic, social, etc) that would restrict or limit the subject participation for the duration of the study.
• Pregnant or breast-feeding women
• Women of childbearing potential not protected by effective contraceptive method of birth control

The above information is not intended to contain all considerations relevant to a patient's potential participation in a clinical trial.