A large-scale, 8-week, open-label, clinical experience trial evaluated the efficacy of the angiotensin II receptor (AT1 subtype) blocker candesartan cilexetil (16 to 32 mg once daily) either alone or as add-on therapy in 6465 hypertensive patients. The study population was 52% female and 16% African American with a mean age of 58 years. It included 5,446 patients who had essential hypertension (HBP) and 1,014 patients who had isolated systolic hypertension (ISH). These patients had either untreated or uncontrolled hypertension (systolic blood pressure [SBP] 140 to 179 mm Hg or diastolic blood pressure [DBP] 90 to 109 mm Hg inclusive at baseline) despite a variety of antihypertensive medications including diuretics, calcium antagonists, angiotensin converting enzyme (ACE) inhibitors, and alpha- or beta-blockers, either singly or in combination. The mean baseline blood pressure for the HBP group was 156/97 mm Hg. Candesartan cilexetil as monotherapy (in 51% of HBP patients) reduced mean SBP/DBP by 18.7/ 13.1 mm Hg. As add-on therapy (in 49% of HBP patients) to various background therapies, candesartan cilexetil consistently reduced mean SBP/DBP further, irrespective of the background therapy: diuretics (17.8/11.3 mm Hg), calcium antagonists (16.6/11.2 mm Hg), beta-blockers (16.5/ 10.4 mm Hg), ACE inhibitors (15.3/10.0 mm Hg), alpha-blockers (16.4/10.4 mm Hg). The mean baseline blood pressure for the ISH group was 158/81 mm Hg. Candesartan cilexetil, as monotherapy (in 34% of ISH patients), reduced SBP/DBP by 17.0/4.4 mm Hg. As add-on therapy (in 66% of ISH patients) to various background therapies, candesartan cilexetil consistently reduced mean SBP/DBP further, irrespective of the background therapy: diuretics (17.4/5.1 mm Hg), calcium antagonists (15.6/3.6 mm Hg), beta-blockers (14.0/4.8 mm Hg), ACE inhibitors (13.4/4.3 mm Hg), and alpha-blockers (11.6/4.5 mm Hg). The further blood pressure lowering effects of candesartan cilexetil as add-on therapy were seen regardless of age, sex, and race. Overall, 6.8% of the 6465 patients withdrew because of adverse events, most commonly headache (6.3%) and dizziness (5.0%). Orthostatic hypotension was infrequent; 0.2% with candesartan cilexetil alone, and 0.8% with candesartan cilexetil as add-on therapy. Thus, candesartan cilexetil either alone or as add-on therapy was highly effective for the control of systolic or diastolic hypertension regardless of demographic background when used in typical clinical practice settings.