INTRODUCTION: Most patients with hypertension require combination therapy to achieve optimal reduction of blood pressure (BP). The angiotensin II receptor blocker, telmisartan, provides 24-hour BP-lowering efficacy and is proven to prevent cardiovascular morbidity in high-risk patients. METHODS: Pooled data from seven randomized controlled trials (3,654 patients with stage 1-2 hypertension) were analyzed to investigate the BP-lowering efficacy of telmisartan 40 or 80 mg (T40 or T80) in combination with hydrochlorothiazide 12.5 or 25 mg (H12.5 or H25) when compared with either placebo or telmisartan monotherapy, relative to patients' baseline BP. BP-lowering efficacy was also assessed in subpopulations. The primary endpoint was the change from baseline in seated trough clinic systolic BP (SBP) and diastolic BP (DBP). RESULTS: In the overall population and across all baseline BP categories, T40/H12.5, T80/H12.5, and T80/H25 resulted in additional BP reductions to those provided by telmisartan monotherapy. In patients with baseline SBP≥170 mmHg, T80/H25 effected a mean SBP change of -39.2 mmHg compared with changes of -25.5 mmHg and -8.3 mmHg observed with T80 and placebo treatment, respectively. Mean DBP changes were -20.4 mmHg T80/H25, -12.2 T80 and -5.9 placebo in patients with baseline DBP≥105 mmHg. T80/H25 also resulted in larger BP reductions than telmisartan monotherapy in black patients with hypertension, irrespective of baseline BP. In patients with hypertension with type 2 diabetes and in patients with moderate or severe renal impairment, both T80/H12.5 and T80/H25 were more effective than monotherapy in reducing BP in all baseline BP categories. CONCLUSION: Combination treatment of telmisartan and hydrochlorothiazide results in large and clinically relevant BP reductions additional to those provided by monotherapy.