Effective antihypertensive therapy is crucial for preventing cardiovascular events; however, blood pressure (BP) control rates remain poor. The objective of this analysis was to determine the efficacy of olmesartan/ amlodipine in age, severity and gender-based subgroups of patients with moderate-to-severe hypertension uncontrolled by amlodipine monotherapy. Patients with uncontrolled BP after 8 weeks' amlodipine 5 mg monotherapy (n ¼ 755) were randomized to continue amlodipine 5 mg or receive olmesartan (10-40 mg) plus amlodipine 5 mg for 8 weeks. Patients whose BP remained suboptimal were uptitrated to olmesartan/ amlodipine 20/5, 40/5 or 40/10 mg. Changes in BP and numbers of controlled patients were calculated separately to assess efficacy in patients aged o65 or X65 years, in those with moderate or severe hypertension, and in males and females. The antihypertensive effects of olmesartan/amlodipine were similar in patients aged o65 and X65 years of age. Compared with patients with moderate hypertension at baseline, those with severe hypertension tended to show higher decreases in BP, but achieved lower goal rates despite this. Females showed larger mean reductions in diastolic (1.61 mm Hg; P ¼ 0.003) and systolic BP (1.72 mm Hg; P ¼ 0.053) than males, independent of age and dose. This gender difference appeared to be higher and more consistent across dose groups for patients o50 years of age, but the difference in the pattern between both age groups was not statistically significant (P ¼ 0.1526). These results suggest that olmesartan/amlodipine is effective and safe in a wide range of patients, regardless of age or hypertension severity. Small differences in responsiveness between females and males may exist, which require further investigation.