Telmisartan is an angiotensin-II receptor blocker that has demonstrated efficacy in the reduction of blood pressure in patients with hypertension. Patients with hypertension commonly require two or more antihypertensives to reduce their blood pressure to safe levels, and the choice of combination therapy should be informed by clinical trial data. Telmisartan is available in fixed-dose combination with hydrochlorothiazide (telmisartan/HCTZ) in doses of 40 mg/12.5 mg and 80 mg/12.5 mg. Telmisartan/HCTZ has been studied in a number of clinical trials in essential hypertension, for the most part using ambulatory blood pressure monitoring. It has been compared with monotherapy in full patient populations and in non-responders, and has been compared with other drug combinations. Telmisartan/HCTZ provides significantly greater reductions in blood pressure than monotherapy, and significantly increases the percentage of patients who achieve target blood pressure. The reduction in blood pressure achieved by adding HCTZ to telmisartan is greater than that achieved by adding HCTZ to atenolol, despite the fact that telmisartan and atenolol monotherapy had similar efficacy. Telmisartan/HCTZ provides significantly greater reductions than losartan plus HCTZ in 24-h mean blood pressure, primarily due to a significantly greater effect in the risky, early morning hours. Telmisartan/HCTZ is effective and well-tolerated in the elderly, diabetics and African-American patients. Ongoing studies are comparing the efficacy of telmisartan/HCTZ with valsartan plus HCTZ and amlodipine plus HCTZ in overweight, hypertensive diabetics and in patients with isolated systolic hypertension - two patient groups who are particularly at risk of target organ damage.